Updated copy (introductio to environmental epidemiology & bio statistics)

COURSE : LCHEH 455
Introduction to Environmental
Epidemiology and Bio-Statistics
LECTURE NOTE PREPARED BY
N. I. BARDA

Introduction to Environmental Epidemiology and Bio-Statistics
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Epidemiology is all about collection of health data on diseases and
other health events, analysis of such data, discuss interpretation
and outcome for action
Series 1 Series 2 Series 3

DEFINITION
Epidemiology is a branch of medicine which deals with the incidence, distribution and possible
control of diseases and other factors relating to health.
Epidemiology is a health care discipline with an important distinction: The “patient” isn’t an
individual, but rather an entire community or population. Specifically, epidemiology uses science,
systems-thinking, and data to determine the underlying causes of different diseases and health
outcomes in a population.
Epidemiologists’ work encompasses a wide range of issues:
 Environmental Issues
 Epidemiologists may study any environmental exposures that contribute to population sickness
or wellness. For example, what’s the local air quality? Are there potent allergens or asthma
triggers? Does the local water supply contain any harmful substances?
 Infectious Diseases
 Epidemiology concerns itself with infectious diseases, as well, which may include anything from
foodborne illness to seasonal flu. Historically, epidemiology has played a vital role in developing a
clear understanding of pandemics such as typhoid and cholera.

Aims and Scopes of Epidemiology
Epidemiology has three main aims, according to the International Epidemiological Association
(IEA):[8]
a) to describe the distribution and magnitude of health and disease problems in human
populations,
b) to identify aetiological factors in the pathogenesis of disease,
c) to provide data essential to the planning, implementation,
and evaluation of services for the prevention, control, and
treatment of disease, and to the setting up of priorities
among those services.

CONCEPT AND PRINCIPLES OF
ENVIRONMENTAL EPIDEMIOLOGY
Environmental Epidemiology is a branch of epidemiology concerned with
determining how environmental exposures impact human health.
This field seeks to understand how various external risk factors may predispose to or
protect against disease, illness, injury, developmental abnormalities, or death.
The principles of Epidemiology are:
1. Distribution- Epidemiology is concerned with the frequency and patterns of Health
events in a population.
2. Determinants- Epidemiology is also used to search for causes and other factors
that influence the occurrence of health related vents

ROLE OF ENVIRONMENTAL
EPIDEMIOLOGY
Environmental Epidemiology is one of the most important tools used in Environmental management decision
making owing to its capacity to assess and monitors environmental hazards in different settings and quantify
their health impact on the population at risk.
In general, environmental epidemiology is an observational rather than an experimental science; scientific
deductions are drawn from patterns of occurrence. Its principal aim is to identify risk factors that can be everted
or reduced so as to prevent or reduce the risk of future diseases and promote public health. To reduce the
health risk presented by hazards, we must seek information on :
 The hazards as they occur in particular environment
 The population groups which are exposed
 The level to which they are exposed
 The health impacts that these hazards could or have
 Potential approaches for reducing exposure
 Acceptability of these approaches in the exposed population

ROLE OF ENVIRONMENTAL
EPIDEMIOLOGY
In this context, environment has been defined broadly as all that which is external to the human host. It can be
divided into physical, biological, social, cultural, etc any or all of which can influence health status of population.
The environment may be considered as representing one or more of the following settings:
 The home environment: exposure may be determined by among other factors, personal or family eating
habits, cooking facilities, drinking water and sanitation facilities, type of building, industrial or farming
activities carried out in or around the home, hobbies, pesticides applied in the home and garden;
 The workplace environment: a person may spend a large part of his or her life in and occupation
environment such as a coal mine or steel works which may be the site of specific environmental problems
and types of exposure; time spent in schools or other educational establishment can also be considered
under this heading;
 The border environment: this can refer to the environment on a regional, national, international or global
scale; associated exposure includes photochemical air pollution, water pollution to rivers or the sea, radiation
as a result of stratospheric ozone depletion, and changes vector-home diseases due to global climate change

OBJECTIVES OF EPIDEMIOLOGY
In the mid 1980s, five major tasks of epidemiology in public health practice were identified:
Public health surveillance, field investigation, analytic studies, evaluation, linkages and policy
development.
Public health surveillance is the ongoing, systematic collection, analysis, interpretation, and
dissemination of health data to help guide public health decision making and action.
Surveillance is equivalent to monitoring the pulse of the community. The purpose of public
health surveillance, which is sometimes called “information for action,” is to portray the
ongoing patterns of disease occurrence and disease potential so that investigation, control,
and prevention measures can be applied efficiently and effectively. This is accomplished
through the systematic collection and evaluation of morbidity and mortality reports and
other relevant health information, and the dissemination of these data and their
interpretation to those involved in disease control and public health decision making

Field investigation: As noted above, surveillance provides information for action. One of
the first actions that results from a surveillance case report or report of a cluster is
investigation by the public health department. The investigation may be as limited as a
phone call to the health-care provider to confirm or clarify the circumstances of the
reported case, or it may involve a field investigation requiring the coordinated efforts of
dozens of people to characterize the extent of an epidemic and to identify its cause.
Analytic studies: Surveillance and field investigations are usually sufficient to identify
causes, modes of transmission, and appropriate control and prevention measures. But
sometimes analytic studies employing more rigorous methods are needed. Often the
methods are used in combination — with surveillance and field investigations providing
clues or hypotheses about causes and modes of transmission, and analytic studies evaluating
the credibility of those hypotheses.

 Evaluation: Epidemiologists, who are accustomed to using systematic and quantitative approaches, have
come to play an important role in evaluation of public health services and other activities. Evaluation is the
process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency,
and impact of activities with respect to established goals
 Linkages: Epidemiologists working in public health settings rarely act in isolation. In fact, field
epidemiology is often said to be a “team sport.” During an investigation an epidemiologist usually
participates as either a member or the leader of a multidisciplinary team. Other team members may be
laboratorians, sanitarians, infection control personnel, nurses or other clinical staff, and, increasingly,
computer information specialists. Many outbreaks cross geographical and jurisdictional lines, so co-
investigators may be from local, state, or federal levels of government, academic institutions, clinical
facilities, or the private sector. To promote current and future collaboration, the epidemiologists need to
maintain relationships with staff of other agencies and institutions. Mechanisms for sustaining such linkages
include official memoranda of understanding, sharing of published or on-line information for public health
audiences and outside partners, and informal networking that takes place at professional meetings.

• Policy development: The definition of epidemiology ends with the following
phrase: “…and the application of this study to the control of health problems.”
While some academically minded epidemiologists have stated that epidemiologists
should stick to research and not get involved in policy development or even make
recommendations, public health epidemiologists do not have this luxury. Indeed,
epidemiologists who understand a problem and the population in which it occurs
are often in a uniquely qualified position to recommend appropriate interventions.
As a result, epidemiologists working in public health regularly provide input,
testimony, and recommendations regarding disease control strategies, reportable
disease regulations, and health-care policy.

NATURE OF ENVIRONMENTAL
RELATED DISEASES
Environmental related diseases (ENVDs) are non-communicable diseases that result
when people are chronically exposed to toxic environmental chemicals. Other
contributory causes of ENVDs includes radiation, pathogens, allergens and
psychological stress. Example of these diseases are:
Lung Cancer due to cigirate smoking or exposure to asbestos
Breathing problem due prolong exposure to wood-burning stoves or inhalation of
carbonated gases.
Asthma
Heart Diseases
Food Poisoning due contamination with toxins or chemical products etc.

HISTORY AND DEVELOPMENT OF ENVIRONMENTAL
EPIDEMIOLOGY
Environmental epidemiology first emerged when Greek and Roman physicians and philosophers perceived links between features
of the immediate environment and ill health. Nevertheless, it was not until much later that these links were evaluated quantitatively.
Early example of this quantitative approach includes the compiled of people , living or working in particular environment, who had
field from a specific disease e.g by Barnadino Ramazzini in the 17th century who wrote the first text describing occupational
diseases ( Ramazzini, 1964, printed).
The first scientific report identifying an environmental cause of cancer was made by Sir Percival Pott who described cancer of
scrotum in English chimney sweeps( Pott, 1775).
The first epidemiology study is also considered to be the first environmental epidemiological study, namely John Snow’s study of
cholera in Lodon and its relationship to water supply location for different households (Smow, 1855). The health effect was in
infectious diseases which spread because of poor sanitation and drainage of sewage into the water supply.
The epidemiological analysis includes identification of where the affected peoples live. As drinking water is a typical environmental
exposure route, Snow was able to demonstrate clearly the association between the source of drinking water and the occurrence of
cholera . This was a truly innovative analysis given that the existence of cholera bacteria had not yet been discovered. John Snow’s
study also shows that at this early stage of epidemiological development, the focus was on preventive action. John Snow did not
know why water caused the disease , But clearly, initial preventive actions can often be taken even though complete information
about the agent that is causing disease is not yet available. In this particular case, John Snow managed to stop the use of the
contaminated water sources. This action reduced morbidity and mortality due to infectious disease long before the specific cause
had been identified, and before antibiotics and vaccine been developed.

HISTORY AND DEVELOPMENT OF ENVIRONMENTAL
EPIDEMIOLOGY
Around the beginning of the 20th century, a series of developments in general medical understanding made
identification of specific causes of environmental diseases easier. Kocch, for instance, identified the role of
bacteria in the 19th century; his postulates for disease causation are still used when the cause of outbreak of disease
is being investigated. Then in the 20th century, asbestos, lead, mercury and other chemical hazards were shown to
be linked to specific diseases. The analysis of the data was crude and the conclusions were often drawn from
studies of small groups of cases. But the notion of making comparisons between an exposed and a non-exposed
population was becoming fairly common.
After the second world war a number of publicized diseases problems and studies brought a new urgency to the
of environmental health, and environmental and epidemiological monitoring became established tools. Examples
can be found for all types of environmental hazards, be they physical, chemical, biological, psycho-social, or safety-
related. For Example:
 After dropping of the nuclear bombs at Hiroshima and Nagasaki, research institute dealing with
epidemiological studies of radiation effect and treatment of the victims was established, The health of the
exposed population was continuously monitored
 In 1952, severe air pollution in London led to a dramatic epidemic of death from heart and lung diseases. A
detailed epidemiological study was carried out ( united Kingdom Ministry of Health, 1952). It established a
quantitative relationship between the severe air pollution and health effect had been observed.

BIOLOGICAL BASIS FOR ENVIRONMENTAL EPIDEMILOGY
Environmental health research is highly unlikely to uncover a toxicant that replicates itself in vitro, but
it can expect to find predictable responses to toxicant exposure that might accurately reflect dose or
early disease and that might be persistent in some cases. In fact, antibodies to carcinogen/DNA adducts
are now beginning to be used in epidemiological studies of populations exposed to cigarette smoke,
chemotherapeutic agents, and workplace chemicals. Biological markers (measurements made from
biological media) are currently of great interest to epidemiologists in the field of environmental health.
Broadly defined for environmental health purposes, biological markers are assays performed on body
fluids, cells, or tissues that indicate, in biochemical or cellular terms, the presence and magnitude of
toxicants or of toxicant/host interactions (including adverse responses). Some markers also indicate the
susceptibility of an individual to adverse responses. In a discussion of general concepts, the term
"biological marker" is preferable to "molecular marker“ or "biochemical marker," because it subsumes
measurements made at the subcellular, cellular, and tissue level. Biological marker data should be
distinguished, on the one hand, from non-biological data, such as historical information, and, on the
other hand, from diagnoses of overt clinical disease. Furthermore, purely physiological data-such as
those obtained by cardiovascular, nerve, or pulmonary function tests-should be excluded, because they
are not derived from biological samples

BIOLOGICAL BASIS FOR ENVIRONMENTAL
EPIDEMILOGY
The use of markers is certainly not new in medical research; it is merely somewhat new to toxicology
and particularly to the epidemiological study of environmental toxicity. Markers have been used, for
example, in nutritional studies (e.g., serum or urinary vitamin concentrations and fecal bile salts),
cardiovascular studies (e.g., serum lipoprotein patterns), and diabetes research (e.g., hemoglobin A1C
measurements). Measures of concentrations of toxicants or their metabolites in body fluids (traditional
biological monitoring) have long been used by epidemiologists to study workplace exposures and, in a
few instances (as in exposure to heavy metals and persistent organo-halogen compounds), to study
community exposures as well.
In this context, markers have five major benefits for environmental epidemiology:
(1) Increased relative risk and statistical power. Biological markers of response constitute early events in
the pathogenesis chain that are generally more common than the ultimate clinical disease. These events
might be necessary but not sufficient for disease causation; for example, not every person with
chromosomal aberration will go on to develop cancer.

EPIDEMIOLOGY
(2) Shorter follow-up times. Markers that reflect early events allow epidemiologists to
reduce the duration of expensive follow-up, and perhaps to use the savings to increase
sample size and statistical power. The ability to observe outcomes sooner also means a
shorter wait for exposed cohorts to "mature."
(3) Reduced misclassification error. The likelihood of error in assigning subjects to
correct exposure categories, when long-term low-level exposures are involved, is
particularly high. This problem is compounded in studies that use group measurements
to classify subjects, such as in epidemiological studies of air pollution based on data
from monitoring stations atop buildings. Unmeasured or unknown factors that alter
exposure/dose relations (e.g., pharmacokinetic variations, exercise, and anatomical
characteristics) contribute to these errors.

EPIDEMILOGY
(4) Delineation of mixture components and conveying exposures.
Biological markers may point out which components of complex toxic
mixtures are reaching and altering target sites. Separating the effects of
mixture components by using ambient-exposure data is a largely statistical
procedure and is restricted by the degree to which specific agents convey
from place to place and time to time.
(5) Linking of epidemiology findings to prevention initiatives.
Epidemiological studies are often criticized for failing to provide means for
timely intervention in affected populations. The further development of
biological markers may allow less "body-counting," and create more direct
opportunities for prevention

APPLICATION OF EPIDEMIOLOGY ON
ENVIRONMENTAL HEALTH
In the developing world, concern focuses on basic sanitation, pure air, and clean water. The
problems are traceable to a large extent to infectious agents, but exposure to toxic substances plays a role.
The World Bank estimates that 1 billion people lack safe water, 1.7 billion are without adequate sanitation,
1.3 billion are exposed to unsafe soot and smoke, and 700 million women and children are exposed to
severe air pollution from cooking fires (World Bank, 1992).
The incomplete understanding of causes of many common chronic diseases in both developed and
developing countries fuels interest in identifying avoidable environmental hazards. Thus, more than 60%
of all cases of birth defects are of unknown or poorly understood etiology (NRC, 1989a), as are many
cases of degenerative neurologic diseases (NRC, 1992a), adult-onset asthma (NRC, 1992b) and other
chronic respiratory diseases (NRC, 1989b), and renal and hepatic diseases. With respect to reproductive
health generally, an array of end points are of concern, ranging from effects on offspring to reproductive
health in males and females, including sexual maturation, onset of menses, menopause, sexual
functioning, and endometriosis. Although these events are often discussed in an atmosphere of high
public concern, suspect environmental factors must be studied with strict adherence to scientific canons
of independent, verifiable research.

APPLICATION OF EPIDEMIOLOGY ON ENVIRONMENTAL HEALTH
Interest in the application of epidemiology to the study of environmental hazards is increasing because
epidemiologic studies can validate the models used in predicting hazards and can characterize the actual and
potential health effects of such exposures.
The same definition of environmental epidemiology is used here, that is, the study of the effect on human health of
physical, biologic, and chemical factors in the external environment. By examining specific populations or
communities exposed to different ambient environments, environmental epidemiology seeks to clarify the
relation between physical, biologic, and chemical factors and human health.
For many chronic, degenerative diseases of potential interest in environmental epidemiology, data on rates of
occurrence (incidence) in defined populations are not routinely collected. In addition, exposure is rarely assessed
in a manner compatible with the needs of epidemiologic investigation. Thus, it is often impossible to determine
whether the incidence of a particular disease has changed in response to a new or changing environmental
exposure. Where a gradient of exposure can be determined, the risk of disease can sometimes be related to dose
in a specially designed study. However, in many instances, diseases of possible environmental etiology cannot be
examined in relation to environmental factors until baseline disease incidences have been determined and
appropriate measures or estimates of exposure have been developed.

HISTORY OF EPIDEMIOLOGY
Epidemiology originates from Hippocrates’ observation more than 2000 years ago that
environmental factors influence the occurrence of disease. However, it was not until the
nineteenth century that the distribution of disease in specific human population groups was
measured to any large extent. This work marked not only the formal beginnings of
epidemiology but also some of its most spectacular achievements. The finding by John Snow
that the risk of cholera in London was related to the drinking of water supplied by a particular
company provides a well-known example; highlights the clustering of cases. Snow’s
epidemiological studies were one aspect of a wide-ranging series of investigations that
examined related physical, chemical, biological, sociological and political processes.
Comparing rates of disease in subgroups of the human population became common
practice in the late nineteenth and early twentieth centuries. This approach was initially applied
to the control of communicable diseases, but proved to be a useful way of linking
environmental conditions or agents to specific diseases. In the second half of the twentieth
century, these methods were applied to chronic noncommunicable diseases such as heart
disease and cancer, especially in middle and high-income countries

In the 1930s and 1940s, epidemiologist extend their methods to noninfectious disease. The
period since world war II has seen an explosion in the development research methods and the
theoretical underpinnings of epidemiology, and has been applied to the entire range of health
related outcomes, behaviors, and even knowledge and attitudes.
During the 1940s and 1950s, several studies were initiated to examine the possible link
between smoking and lung cancer. One of them was conducted by Doll and Hills, their work
was preceded by experimental studies on the carcinogenicity of tobacco tars and by clinical
observations linking tobacco use and other possible factors to lung cancer. By using long
term cohort studies, they were able to establish the association between smoking and lung
cancer

During the 1960s and early 1970s health workers applied epidemiologic methods to
eradicate naturally occurring smallpox worldwide. In the 1980s epidemiology was extended
to the studies of injuries and violence, in 1990s related fields of molecular and genetic
epidemiology and took the roots.
Epidemiology in its modern form is a relatively new discipline and uses quantitative
methods to study diseases in human populations to inform prevention and control efforts.
For example, Richard Doll and Andrew Hill studied the relationship between tobacco use
and lung cancer, beginning in the 1950s.
Today, public health workers throughout the world accept and use epidemiology regularly to
characterize the health of their communities and to solve day-to-day problems, large and
small.

CONTRIBUTION OF SOME PIONEERS
IN EPIDEMIOLOGICAL WORK
 Circa 400 B.C Hippocrates suggested that environmental and host factors such as behaviors might
influence the development of disease.
John Graunt 1662 ( London Councilman ): published a landmark analysis and quantify patterns of
birth, death, and diseases occurrence, noting disparities between males and females, high infants
mortality, urban/ rural differences, and seasonal variations.
Willian Farr 1800: Systematically collecting and analyzing Britain’s mortality statistics.
John Snow 1854 ( Father of the field of epidemiology): Epidemiological studies of chronic diseases
began around the mid-19th century.
In the Mid-and late 1800s, epidemiological methods begins to be applied in the investigation of
disease occurrence.
Thomas Syndenham (1624-1689 ): Recognized as a founder of clinical medicine and epidemiology,
and emphasized detailed observations of patients and accurate record keeping.

CONTRIBUTION OF SOME PIONEERS
IN EPIDEMIOLOGICAL WORK
James Lind ( 1700’s) Designed first experiments to use a
concurrently treated control group.
Edward Jenner ( 1749-1823 ) Pioneered clinical trials for vaccination
to control spread of smallpox, Janner’s work influenced many
others, including Louis Pasteur who developed vaccines against
rabies and other infectious diseases.
Ignas Semmelweis (1840’s): Pioneered handwashing to help prevent
the spread of septic infections in mothers following birth.

DEFINITION OF TERMS USED IN EPIDEMIOLOGY
Some epidemiological terms commonly used to describe health-related states in a population are listed and defined
below.
• “Outbreak” refers to the occurrence of new case(s) of disease in a previously unexposed population.
• “Cluster" refers to an aggregated group of cases believed to be present in a higher number than expected, even
though the expected number may not be known.
• Epidemic” refers to the spread of disease agent, pathogen or infection from exposed persons to unexposed
persons in a population. Often the term epidemic is used to describe the rapid or sudden occurrence of disease,
disease agent or health condition in a population above what is normally expected for that population in a certain
geographical area.
• “Endemic” refers to ongoing presence of disease agent or health condition in a population (with or without
symptoms). It is possible for disease to remain indefinitely in a population, as long as there are susceptible
people, including carriers. Endemic refers to the constant presence and/or usual prevalence of a disease agent,
health condition or infectious agent in a population within a geographic area.
• Sporadic” refers to a disease agent or health condition that occurs infrequently or irregularly in a population.
• Hyper-endemic” refers to persistent high levels of occurrence of a disease agent or health condition in a
population.

DEFINITION OF TERMS USED IN EPIDEMIOLOGY
• Pandemic” refers to an epidemic that has spread over several countries and continents, usually affecting a large number of
people.
• Epidemic proportion” has been used to describe large numbers of cases of chronic disease in a population (high proportion
or prevalence of chronic disease).
• Incident – event of interest, a specific disease or health-related event, e.g. birth, death, lung cancer, diarrhoea
• Incidence - the occurrence of new cases of disease in members in a population. Focus is on changes in health state in the
population.
• Incidence rate - the measure of occurrence of new cases of disease per unit of person-time. The number of new cases of
disease divided by the sum of the person time over the period of interest.
• Prevalence Odds - ratio of diseased to non-diseased or the ratio of the proportion of the population that has disease to the
proportion that does not have the disease; where diseased and non-diseased refers to the occurrence of a specified illness, which
is not the same as absence of all illness in non-diseased.
• Rate - is the number of cases divided by the size of the population per unit time. Expressing counts as rate give context to the
numbers by relating the number of cases to the size of the population in which the counts are made of cases that occurred,
within a specified time period,
• Sensitivity - the ability of a test to correctly identify “true positives”, persons with disease. A test with a sensitivity of 100% has a high sensitivity
and low probability of a Type errors

DEFINITION OF TERMS USED IN EPIDEMIOLOGYD
• Specificity - the ability of a test to correctly identify “true negatives”,
persons without disease. A test with a specificity of 100% has a high
specificity and a low probability of a Type I error = 1-α.
• Standardization – is a common technique used in epidemiology to control
for confounding and for summarization of occurrences and effects.

LIST OF TOOLS USE IN EPIDEMIOLOGICAL SURVEY
BASIC ELEMENTS OF EPIDEMIOLOGICAL STUDIES
The basic elements of an epidemiological study can be characterized as follows:
• formulation of the study question or hypothesis
• selection of study populations and study samples
• selection of indicators of exposure
• measurement of exposure and disease
• analysis of the relationship between exposure and disease
• evaluation of the role of bias
The basic tools use in the conduct of environmental epidemiological survey include the following:
Proportions, ratios, rates, prevalence, incidence, study designs, bias, confounding, effect modification,
odds and risk ratios, statistical power, and confidence intervals

USES OF EPIDEMIOLOGICAL SURVEY
• Epidemiological methods are used for diseases surveillance to identify which hazards are the
most important, and also uses to identify the risk factors which may represent critical
control points in the food production system.
• For community diagnosis of the presence, nature and distribution of health and
disease among the population, and the dimensions of these in incidence, prevalence, and
mortality; taking into account that society is changing and health problems are changing. To
study the workings of health services
• Epidemiology has several uses that are really important to understanding diseases and how
they impact different communities. It helps us assess community health by finding out
whether certain populations are at higher risk and whether health services are prepared to
deal with health issues.

WHAT IS PUBLIC HEALTH
Public health has been defined as "the science and art of preventing disease”, prolonging
life and improving quality of life through organized efforts and informed choices of
society, organizations (public and private), communities and individuals. Analyzing the
determinants of health of a population and the threats it faces is the basis for public health.
The public can be as small as a handful of people or as large as a village or an entire city; in
the case of a pandemic it may encompass several continents. The concept of health takes
into account physical, psychological, and social well-being.
Public health is an interdisciplinary field. For example, epidemiology, biostatistics, social
sciences and management of health services are all relevant. Other important sub-fields
include environmental health, community health, behavioral health, health economics,
public policy, mental health, health education, health politics, occupational safety, disability,
gender issues in health, and sexual and reproductive health

SURVEILLANCE
MONITORING
ANALYSIS
OUTBREAKS
RESPONCE
DISEASES
PREVENTION
COMMUNICATI
ON
EMMEGENCY
PREPARDNESS
RECOVERY
ENVIRONMENT
AL HEALTH
RESEARCH
HEALTH
PROMOTION
PUBLIC HEALTH IS ALL ABOUT

EXPOSURE MONITORING/ ASSESSMENT
Exposure Assessment is the process of characterizing, estimating, measuring and
modeling the magnitude, frequency and duration of contact with an agent as well as
the number and characteristics of the population exposed.
The possible route of exposure are: Inhalation, if the contaminant is present in the
air, ingestion through food, drinking or hand-to-mouth behavior; and dermal
absorption, if the contaminant can be absorbed through the skin.
Exposure assessment is one of the four major steps in risk assessment, others
include hazard identification, dose-response assessment, and risk characterization
Personal exposure monitoring is a way of measuring a worker’s exposure level to a
hazard. Common hazards that may require exposure monitoring include: Physical
hazards such as radiation, heat, cold, vibration and noise.

HEALTH SURVEILLANCE
Health surveillance is a system of ongoing health checks. These health checks may be required by law for employees who are
exposed to noise or vibration, ionizing radiation, solvents, fumes, dusts, biological agents and other substances hazardous to
health, or work in compressed air.
Health surveillance is important for:
• to raise concerns about how work affects their health
• highlighting lapses in workplace control measures, therefore providing invaluable feedback to the risk assessment
• providing an opportunity to reinforce training and edudetecting ill-health effects at an early stage, so employers can
introduce better controls to prevent them getting worse
• providing data to help employers evaluate health risks
• enabling employees cation of employees (eg on the impact of health effects and the use of protective equipment)
Your risk assessment should be used to identify any need for health surveillance. You should not use health surveillance as a
substitute for undertaking a risk assessment or using effective controls.
Health surveillance can sometimes be used to help identify where more needs to be done to control risks and where early
signs of work-related ill health are detected, employers should take action to prevent further harm and protect employees.

STEPS AND METHOD OF AN OUTBREAK INVESTIGATION
Investigating an outbreak/ epidemic is a set of procedures used to identify the cause responsible for the disease, the people
affected, the circumstances and mode of spread of the disease, and other relevant factors involved in propagating the
epidemic, and to take effective actions to contain and prevent the spread of the disease. Below are some of the steps to follow
in outbreak investigation:
• Prepare for field work.
• Establish the existence of an outbreak.
• Verify the diagnosis.
• Construct a working case definition.
• Find cases systematically and record information.
• Perform descriptive epidemiology.
• Develop hypotheses.
• Evaluate hypotheses epidemiologically.
• As necessary, reconsider, refine, and re-evaluate hypothesis
• Compare and reconcile with laboratory and or/ or environmental studies
• Implement control and prevention measures
• Initiate and maintain surveillance
• Communicate findings

HOW TO INVESTIGATE THE HEALTH
IMPACT OF LOCAL POLLUTION
Air pollution is linked to health problems in the respiratory, cardiovascular, reproductive,
neurological, and immune systems. For example, people with asthma can have difficulty
breathing if air pollution is high, and prenatal and early childhood air pollution exposure is
linked with neurobehavioral problems. Long-term exposure can cause cancer. So investigation
on the role air pollution plays in the development of various diseases, biological effects on the
body, and groups who are most susceptible is of greater interest.
The investigator should be able to make adequate plan, taking into cognizance, the selection
of appropriate methods and tools. Input data are required on, for example: (1) the level of air
pollution, (2) the exposed population, and (3) the health outcome affected (concentration
response functions). The selection of the method may depend on data availability or may
determine the data requirements. In addition, different tools will entail different workloads and
require different levels of expertise.

Decision-tree showing the sequence of choices and feedback
loops when conducting an Air Pollution High Risk Assessment-(HRA)

USES OF ENVIRONMENTAL EPIDEMIOLOGICAL HEALTH NEEDS
ASSESSMENT IN POLICY AND MANAGEMENT
Health needs assessment (HNA) is an essential tool to inform commissioning and
service planning, and can be defined as a systematic method of identifying the unmet
health and health care needs of a population, and making changes to meet those unmet
needs. HNA allows for appropriate targeting of resources, and often involves working in
partnership with other agencies, communities and service users. Indeed, HNA can be an
excellent opportunity to involve stakeholders in service planning and increase ownership
and sustainability. HNA may focus on specific diseases, population groups, procedures or
interventions.
Environmental epidemiology has the advantage of being able to study and possibly
prevent health impairment which has not yet led to disease. Hence it has a great
potentials contribution toward prevention

DEFINING HEALTH NEEDS ASSESSMENT
Dahlgren and Whitehead Model

CONCEPT OF DEMOGRAPHIC STUDY
Demographics help us understand the size, status, and behavior of populations. Broadly defined as the study of
the characteristics of populations. It provides a mathematical description of how those characteristics change over
time.
Demographic analysis is the study of a population based on factors such as age, race, and sex. Demographic data
refers to socioeconomic information expressed statistically including employment, education, income, marriage
rates, birth and death rates, and more.
The major components of demography study are :
• Mortality
• Fertility
• Migration
DEMOGRAPHIC INDICATORS INCLUSES: Crude Birth Rate, General Fertility Rate, Crude Death Rate
and Infant Mortality rate, Life Expectancy, Total Fertility, Gross Reproduction Rate and Net Reproduction Rate

Some terms used in Demography
 Population: is a complete set of items or subjects which can be studied.
 Target population: A collection of items that have something in common for which we wish to
draw conclusions at a particular time.
 Relationship: This is define as the way in which two or more people or groups regard and behave
towards each other.
 Association: A connection or cooperative link between people or organization. It is a group or
organization to which you may belong. Eg Environmental Health Officer’s Association.
Association is an organization of persons having common interest, purposes etc,
 Interaction: Is a degree to which you engage one-to-one with colleagues, while interactions are one
way to raise your visibility, it is inevitable that some interactions will begin to build a relationship.

CRITERIA FOR CAUSALITY
Causality concerns relationships where a change in one variable necessarily results in a change in another
variable. There are three conditions for causality: covariation, Temporal precedence, and control for third
variables.
There are three criteria generally considered as requirements for identifying a causal effect:
Empirical Association: In science, an empirical relationship or phenomenological relationship is a
relationship or correlation that I supported by experiment and observation but not necessarily
supported by theory
Temporal Priority of the independent variables: Temporal priority of the independent variables/ time
order, making sure that the independent variables come before the dependent variables. Eg the
incidence must occurred before the effect.
Non-spuriousness : This is defined as a relationship between two variables that is not due to variation in
a third variables ( the relationship between X and Y cannot occur by chance alone). When this third
variable, an extraneous variable, causes the variation, it is said to have created a spurious relationship
between the independent and dependent variables.

MEASUREMENT OF HEALTH IN A
POPULATION
Summary measures of population health (SMPH) combine information on mortality and non-fatal
health outcomes to present the health of a particular population in a single numerical index.
Traditionally, mortality statistics have been the solid basis of population health measures.
Health indicators are quantifiable characteristic of a population which researcher use as supportive
evidence for describing the health of a population, other factors could be used to measure the health
of a population such as economic status, geography, gender and ethnicity. However, population
health can also be explored across different diseases or age groups. In addition, risk factors play an
important part in determine population health, and could provide basis to segment the population.
Mortality and life expectancy are two basic measures of population health. The number of death
that occur in a population during a period of time ( usually 1 year ) divided by the size of the
population is the population’s crude mortality.

HEALTH MEASUREMENT INSTRUMENTS:
METHODS AND CHOICES
For the choice of instrument, one need to consider evaluative instruments (those designed to measure longitudinal
change over time) another property is required: the instrument must detect clinically important changes over time,
even if those changes are small. This has been referred to as sensitivity to change or responsiveness.
 Validity: and reliability are perhaps the most important criteria that should be used in the development and
application of health measurement instruments. Validity is concerned with whether the indicator actually does
measure the underlying attribute or not. The assessment of validity involves assessment against a standard
criterion.
 Reliability: (consistency or reproducibility) is a measure of the proportion of the variability in scores which is due
to true differences between individuals. A measure is judged to be reliable when it is relatively free of
measurement error and thus consistently produces the same results, particularly when applied to the same
subjects at different time periods.
The uses of health indicators should contribute to overall population health goals, namely improving the health of
populations and reducing health inequalities. Health indicators support this goal through the following key
applications: advocacy, accountability, system management, quality improvement, and research

Environmental Monitoring is defined as the observation of the presence of
harmful factors such as toxins, bacteria, chemicals and other pollutants in a specific
location.
According to P. Venugopala Rao, “Environmental monitoring means collecting a
representative portion of water, waste or air from an area to ascertain its quality and
characteristics.”
46

Objectives of Environmental
Monitoring
☺ To establish a base-line of exposure.
☺ To co-relate with a suspected source of contamination.
☺ To estimate the changes in levels of the pollutants in the environment.
☺ Confirming and reconfirming the success of the pollution control measures.
☺ Collection of meaningful and relevant information.
☺ Know the nature and degree of pollution from various sources.
☺ Recommendation of improves mitigation measures to be undertaken. 47

CONCEPT OF ENVIRONMENTAL
MONITORING
Environmental monitoring is a tool to assess environmental conditions and trends, support
policy development and its implementation, and develop information for reporting to national
policymakers, international forums and the public. It is a tools and techniques designed to observe an
environment, characterize its quality, and establish environmental parameters, its also involves the
assessment of the quality of the environment in order to control the risk of pollution.
Environmental monitoring includes collection of environmental media (air, water, soil) for chemical
analysis, or may include real-time monitoring using devices
The main objectives of environmental monitoring is to manage and minimize the impact an
organization’s activities have on an environment, either to ensure compliance with laws and regulations
or to mitigate risks of harmful effects on the natural environment and protect the health of human
beings.

CONCEPT OF BIOLOGICAL
MONITORING
Biological monitoring is a biological assessment of exposed organisms in order to detect adverse effects, which
may indicate their exposure to the level of toxicity due to such substances in their environment.
The purpose of biological monitoring of exposure is to assess health risk through the evaluation of internal
dose, achieving an estimate of the biologically active body burden of the chemical in question. Its rationale is to
ensure that worker exposure does not reach level capable eliciting adverse effect.
Biological monitoring can be used to indicate how much of a chemical has entered the body. It involves
measuring the chemical the workers are exposed to at work ( or its breakdown products ) in a sample of breath,
urine or blood.
There are three main exposure pathways to chemicals: Inhalation(Lungs), Dermal (Skin) and Gastrointestinal
(Ingestion). Biological monitoring considers the overall systemic exposure ( internal dose) and effect (biological
effective dose) regardless of the source or pathway.

SURVEILLANCE AND SCREENING
The fundamental purpose of screening is early diagnosis and treatment of the individual and thus has a clinical focus. The
fundamental purpose of surveillance is to detect and eliminate the underlying causes such as hazards or exposures of any
discovered trends and thus has a prevention focus.
Surveillance is defined as the ongoing and systematic collection, analysis, interpretation, and dissemination of data about cases of
a disease and is used as a basis for planning, implementation, and evaluating disease prevention and control activities. In summary, it
is collection and analysis of data for action.
The Purpose of Surveillance are:
• To monitor disease trend so as to help planning
• To detect and investigate outbreaks to institute control measures
• Identify groups at higher risk to apply additional preventive measures
• Evaluate the impact of preventive control measures on disease incidence
Screening are test that look for diseases before the symptoms manifest. It helps in early findings of diseases for quicker
intervention, to about complication, and it is done either by the doctor himself through physical examination ( i.e measurement of
height, weight, waist circumference, arm circumference, blood pressure (BP)etc, or by the laboratory officer using different
techniques.

MEASURES OF HEALTH STATUS,
QUALITY OF LIFE AND HEALTH CARE
• In 1948, WHO defined health as “a state of complete physical, mental and social
well-being, and not merely the absence of disease”. Health can be considered in
terms of a person’s body structure and function and the presence or absence of
disease or signs (health status); their symptoms and what they can and cannot do
i.e. the extent to which the condition affects the person’s normal life (quality of
life).
• Health care is the prevention, treatment, and management of illness and the
preservation of health through the services offered by health care organisations and
professionals. It includes all the goods and services designed to promote health,
including preventive, curative and palliative interventions, whether directed to
individuals or to populations.

MEASURES OF HEALTH STATUS,
QUALITY OF LIFE AND HEALTH CARE
Health status can be measured using pathological and clinical measures and is usually observed by
clinicians or measured using instruments.
Types of disease measurement include:
• Signs - blood pressure, temperature, X-ray, tumour size
• Symptoms - disease specific checklists
• Co-morbidity - Charlson Index, ICED- index of co-existing disease (looks at both disease
severity and functional severity), adverse events – pain, bleeding, readmission, complications (e.g.
using Clavien-Dindo Classification of Surgical Complications).
It is always best to use an existing measure which has been tried and tested rather than inventing a
new one. Use an existing standardised measure with proven reliability, validity and responsiveness.

THE CYCLE OF CHANGE AND IMPACT DRIVEN

HEALTH IMPACT EVALUATION
Impact is defined as the immediate effect that health promotion programs have on
people, stakeholders and settings to influence the determinants of health. Health promotion
programs may have a range of immediate effects on individuals and on social and physical
settings
For individuals, the immediate effects include improved health knowledge, skills and
motivation, and changes to health actions and behaviour. In relation to settings, these include
the creation of new organisations, programs and services to promote health, reductions in
physical health risks and improvements to the physical environment to protect health and
health promoting changes to organisational policies and practices. Integrated health promotion
programs should specify impact indicators for program activities. These indicators should
specify the type of change that is expected and the percentage of people or settings for which
that change is anticipated

HEALTH IMPACT EVALUATION
The key tasks in undertaking impact evaluation include:
• Identifying the impact indicators to be used
• Establishing the target levels for the impact indicators
• Identifying the information to be collected and methods of doing this
• Designing the evaluation to increase the likelihood that observed effects can be
attributed to the health promotion program
• Implementing the impact assessment.
• Reporting the impact assessment

STATICTICS
Statistics: A field of study concerned with the collection, organization and
summarization of data, and the drawing of inferences about a body of data
when only part of the data are observed.
Biostatistics: An application of statistical method to biological phenomena.

TYPES OF STATISTICS
• Descriptive statistics :use to organize
and describe a sample /population
• Inferential statistics :use to
extrapolate (estimate ) from a sample to
larger population

USES OF BIOSTATISTICS
• Hospital utility statistics
• Resource allocation
• Vaccination uptake
• Magnitudes of a disease/condition
• Assessing risk factors
• Disease frequency
• Making diagnosis and choosing an
• appropriate treatment (implicit/probability)

OTHER USES OF STATISTICS
1) Uses of statistics in Government: The importance of statistics in government is utilized by making
judgments about health, populations, education, and much more. It may help the government to
check out what education schedule can be beneficial for students.
2) Uses of statistics in Biological Science: Statistical analysis provide crucial insight into many biological
processes. Basic statistical concepts help biologists correctly prepare experiments, verify conclusions
and properly interpret results.
3) Uses of statistics in physical science: Statistics in physical science is principally concerned with the
analysis of numerical data. It uses mathematical tools for dealing with large populations and
approximations, in solving physical problems. It can also help in describing a wide variety of fields.
4) Uses of statistics in Business: Statistical research in business enables managers to analyze past
performance, predict future business practices and lead organizations effectively. Statistics can
describe markets, inform advertising, set prices and respond to changes in consumer demand.

OTHER USES OF STATISTICS
• Uses of statistic in Economy: Statistics for economics concerns itself with the
collection, processing, and analysis of specific economic data. It helps us
understand and analyze economic theories and denote correlations between
variables such as demand, supply, price, output etc. Let us understand this in some
detail.
• Uses of statistics in Environmental Health: Specific applications of statistical
analysis within the field of environmental science include earthquake risk
analysis, environmental policymaking, ecological sampling planning,
environmental forensics. ... Inferential statistics is used to make inferences about
data, test hypotheses or make predictions.

Data: is a collection of facts, figures, objects, symbols, and events gathered from different
sources. Organizations collect data to make better decisions. Without data, it would be
difficult for organizations to make appropriate decisions, and so data is collected at various
points in time from different audiences.
For instance, before launching a new product, an organization needs to collect data on
product demand, customer preferences, competitors, etc. In case data is not collected
beforehand, the organization’s newly launched product may lead to failure for many reasons,
such as less demand and inability to meet customer needs.
Although data is a valuable asset for every organization, it does not serve any purpose
until analyzed or processed to get the desired results.
WHAT IS DATA

METHODS OF DATA COLLECTION
• Primary Data Collection Methods : Primary data is collected from the first-hand
experience and is not used in the past. The data gathered by primary data collection
methods are specific to the research’s motive and highly accurate. Primary data
collection methods can be divided into two categories: quantitative methods and
qualitative methods.
• Secondary Data Collection Methods: Secondary data is the data that has been
used in the past. The researcher can obtain data from the sources, both internal
and external, to the organization.

A) INTERNAL SOURCES OF SECONDARY DATA:
1. Organization’s health and safety records
2. Mission and vision statements
3. Financial Statements
4. Magazines
5. Sales Report
6. CRM Software
7. Executive summaries
B) External sources of secondary data:
1. Government reports
2. Press releases
3. Business journals
4. Libraries
5. Internet
The secondary data collection methods, too, can involve both quantitative and qualitative
techniques. Secondary data is easily available and hence, less time-consuming and expensive as
compared to the primary data. However, with the secondary data collection methods, the
authenticity of the data gathered cannot be verified.
METHODS OF DATA COLLECTION

SYSTEMS FOR COLLECTING DATA
1.Regular system (routine data collecting
system): Registration of events as they
become available.
2.Ad hoc system (non-routine): A form of
survey to collect information that is not
available on a regular basis.

1) ROUTINE SYSTEM:
• Census: enumeration of all individuals in a country on
a fixed day.
• Vital registrations: birth, deaths, marriage, divorce, ete.
• Disease notification: international notification, like
cholera, national notification like polio, cholera, hepatitis
notification is from district level to national level to
international level.
• Disease registry: TB, cancer, stroke, birth defects
• Medical records: schools, colleges, industries
• Hospital records
• Environmental health records

2. NON-ROUTINE
1. Disease surveillance: Polio, malaria, AIDS= it is important for
control, prevention and eradication.
2. Surveys: nutritional status by interviewing examination or
postal enquiry based.
3. Social schemes: medical insurance, sickness absenteeism,
disability benefits, welfare schemes
4. Economic data: Consumption of goods, export and import,
drugs, employment = helps panning commission for formulation of
health policies
5. Demographic data: population movement, major epidemics

DEFINITION OF SOME STATISTICAL TERMS
1. Deviation: is a measure that is used to find the difference between the observed value and expected
value of a variable.
2. Mean Deviation: Is defined as a statistical measure that is used to calculate the average deviation from
the mean value of the given set.
The formula to calculate the mean deviation for the given data set is given below.
• Mean Deviation = [Σ |X – µ|]/N
• Here,
• Σ represents the addition of values
• X represents each value in the data set
• µ represents the mean of the data set
• N represents the number of data values
• | | represents the absolute value, which ignores the “-” symbol

3. Standard deviation: is a measure of the amount of variation or dispersion of a set of values. A low
standard deviation indicates that the values tend to be close to the mean of the set, while a high standard
deviation indicates that the values are spread out over a wider range.
4. semi-interquartile range: is one-half the difference between the first and third quartiles. It is half the
distance needed to cover half the scores. The semi-interquartile range is affected very little by extreme
scores. This makes it a good measure of spread for skewed distributions. It is obtain by evaluating
Q3-Q1
2
5. Range: Is the difference between the maximum and the
minimum data values. R = XL- XS, where XL = is the largest value and XS = is the smallest
value.
6. Variance: variance is the average of the squares of the deviations taken from the mean

DEFINITION OF SOME STATISTICAL
TERMS
7. Standard error of the mean (SEM): Quantifies the precision of the mean. It is a
measure of precision of a sample statistic. Tells us how precise our estimate of the
parameter is. It is a measure of how far your sample mean is likely to be from the true
population mean.
8. Variables: A variable is any characteristic that varies from one individual member of
the population to another. Examples of variables for humans are height, weight,
number of siblings, sex, marital status, and eye color.
9. Random Variables: A random variable is a variable whose value is a numerical
outcome of a random phenomenon.

10. Discrete variables. Some variables, such as the numbers of children in family, the
numbers of car accident on the certain road on different days, or the numbers of
students taking basics of statistics course are the results of counting and thus these are
discrete variables. Typically, a discrete variable is a variable whose possible values are
some or all of the ordinary counting numbers like 0, 1, 2, 3, . . . . As a definition, we can
say that a variable is discrete if it has only a countable number of distinct possible
values.
11. Continuous variables. Quantities such as length, weight, or temperature can
principle be measured arbitrarily accurately. There is no invisible unit. Weight may be
measured to the nearest gram, but it could be measured more accurately, say to the
tenth of a gram. Such a variable, called continuous, is intrinsically different from a
discrete variable.
12. Probability: The probability of a particular outcome is the proportion of times that
outcome would occur in a long run of repeated observations.

CONCEPT OF RANDOMNESS
Definitions: Randomness means different things in various fields, community.
It means lack of pattern or predictability in events. In other word, Randomness
is refers according to a social science and mathematics as chance factors
occurring in a manner that the individual events.
Randomness has a very important applications in many areas of mathematics.
In statistics, the selection of a random sample is important to ensure a study in
conducted without bias. A simple random sample is obtained by numb erring
every member of the population of interest, and assigning each member a
numerical label.

PROBABILITY USING RELATIVE
FREQUENCY
Relative frequency or experimental probability is calculated from the number of times
an event happens, divided by the total number of trials in an actual experiment.
Relative frequency is used when probability is being estimated using the outcomes of
an experiment or trial, when theoretical probability cannot be used.
For example, when using a biased dice, the probability of getting each number is no
longer 1/6. To be able to assign a probability to each number, an experiment would
need to be conducted. From the experimental results, the relative frequency could be
calculated.
The more times that an experiment has been carried out, the more reliable the relative
frequency is as an estimate of the probability.

Example
Ella rolls a dice and records the number of times she scores a six. Find the relative frequency
that Ella rolls a six on her dice.
PROBABILITY USING RELATIVE FREQUENCY
Number of rolls 10 20 30 40 50
Total number of
sixes
2 3 6 8 9
Ella’s results will give different estimates of the probability, depending on which total is
selected.
For example, in the first 10 rolls, the relative frequency of scoring 6 is 2 /10 =0.2, but in the
first 20 rolls, the relative frequency of scoring 6 is 3 / 20 =0.15.
The most accurate estimate of the probability is found by using the highest number of rolls,
which gives 9 / 50 = 0.18

LAW OF TOTAL PROBABILITY AND BAYES' THEOREM
In probability theory, the law of total probability is a fundamental rule relating marginal probabilities to
conditional probabilities. It expresses the total probability of an outcome which can be realized via
several distinct events.
There are three main laws associated with basic probability: the addition law of probability, the
multiplication law of probability, and the Binominal law of probability.
Basic Probability Rules
Probability Rule One (For any event A, 0 ≤ P(A) ≤ 1)
Probability Rule Two (The sum of the probabilities of all possible outcomes is 1)
Probability Rule Three (The Complement Rule)
Probabilities Involving Multiple Events.
Probability Rule Four (Addition Rule for Disjoint Events)

CONDITIONAL PROBABILITY
Conditional probability is defined as the likelihood of an event or outcome occurring based on the occurrence of a
previous event or outcome. The conditional probability of an event B is the probability that the event will occur given
the knowledge that an event A has already occurred. This probability is written P(B|A), notation for the probability of B
given A. In the case where events A and B are independent (where event A has no effect on the probability of event B), the
conditional probability of event B given event A is simply the probability of event B, that is P(B).
From this definition, the conditional probability P(B|A) is easily obtained by dividing by P(A):
Examples 1
• In a card game, suppose a player needs to draw two cards of the same suit in order to win. Of the 52 cards, there are 13
cards in each suit. Suppose first the player draws a heart. Now the player wishes to draw a second heart. Since one heart
has already been chosen, there are now 12 hearts remaining in a deck of 51 cards. So the conditional probability P(Draw
second heart|First card a heart) = 12/51.

CONDITIONAL PROBABILITY
EXAMPLE 2
Suppose an individual applying to a college determines that he has an 80% chance
of being accepted, and he knows that dormitory housing will only be provided for
60% of all of the accepted students. The chance of the student being accepted and
receiving dormitory housing is defined by
P(Accepted and Dormitory Housing) = P(Dormitory Housing|Accepted)P(Accepted)
= (0.60)*(0.80) = 0.48.

METHODS OF DATA ANALYSIS
What Is Data Analysis?
• Data analysis is the process of collecting, modeling, and analyzing data to
extract insights that support decision-making. There are several methods and
techniques to perform analysis depending on the industry and the aim of the
analysis.
• 7 Essential Types Of Data Analysis Methods
I. Cluster Analysis
II. Cohort Analysis
III. Regression Analysis
IV. Factor Analysis
V. Neural Analysis
VI. Text Analysis
VII. Data Mining

1. Cluster analysis
The action of grouping a set of data elements in a way that said elements are more similar (in a
particular sense) to each other than to those in other groups – hence the term ‘cluster.’ Since there is
no target variable when clustering, the method is often used to find hidden patterns in the data. The
approach is also used to provide additional context to a trend or dataset.
2. Cohort analysis
This type of data analysis method uses historical data to examine and compare a determined segment
of users' behavior, which can then be grouped with others with similar characteristics. By using this
data analysis methodology, it's possible to gain a wealth of insight into consumer needs or a firm
understanding of a broader target group.
3. Regression analysis
The regression analysis uses historical data to understand how a dependent variable's value is
affected when one (linear regression) or more independent variables (multiple regression) change or
stay the same. By understanding each variable's relationship and how they developed in the past, you
can anticipate possible outcomes and make better business decisions in the future.

4. Neural networks
The neural network forms the basis for the intelligent algorithms of machine learning. It is a form of
data-driven analytics that attempts, with minimal intervention, to understand how the human brain
would process insights and predict values. Neural networks learn from each and every data
transaction, meaning that they evolve and advance over time
5. Factor analysis
The factor analysis, also called “dimension reduction,” is a type of data analysis used to describe
variability among observed, correlated variables in terms of a potentially lower number of
unobserved variables called factors. The aim here is to uncover independent latent variables, an
ideal analysis method for streamlining specific data segments.
6. Data mining
A method of analysis that is the umbrella term for engineering metrics and insights for additional
value, direction, and context. By using exploratory statistical evaluation, data mining aims to
identify dependencies, relations, data patterns, and trends to generate and advanced knowledge.
When considering how to analyze data, adopting a data mining mindset is essential to success - as
such, it’s an area that is worth exploring in greater detail.

7. Text analysis
Text analysis, also known in the industry as text mining, is the process of taking large sets of
textual data and arranging it in a way that makes it easier to manage. By working through this
cleansing process in stringent detail, you will be able to extract the data that is truly relevant
to your business and use it to develop actionable insights that will propel you forward.

SOME OF THE DATABASE/ SOFTWARES USE IN STATISTICAL
ANALYSIS
1. SPSS: is short for Statistical Package for the Social Sciences, and it’s used by various kinds of
researchers for complex statistical data analysis. The SPSS software package was created for the
management and statistical analysis of social science data. It was originally launched in 1968 by SPSS
Inc., and was later acquired by IBM in 2009.
SPSS is used by market researchers, health researchers, survey companies, government entities,
education researchers, marketing organizations, data miners, and many more for processing and
analyzing survey data, such as you collect with an online survey platform like Alchemer.
2. Epi Info: is a public domain suite of interoperable software tools designed for the global community
of public health practitioners and researchers. It provides for easy data entry form and database
construction, a customized data entry experience, and data analyses with epidemiologic statistics, maps,
and graphs for public health professionals who may lack an information technology background. Epi
Info is used for outbreak investigations; for developing small to mid-sized disease surveillance systems;
as analysis, visualization, and reporting (AVR) components of larger systems; and in the continuing
education in the science of epidemiology and public health analytic methods at schools of public health
around the world.

TYPES OF EPIDEMIOLOGICAL STUDIES
Epidemiological studies generally fall into four broad categories:
• Cross sectional studies: This studied measure exposure and diseases status at the same time, and are better
suited to descriptive epidemiology than causation.
• Case control studies: Also known as referent study, is a type of observational study in which two existing
groups differing in outcome are identified and comparted on the basis of some suspected causal attribute.
• Cohort Studies: Cohort studies are a type of longitudinal study—an approach that follows research
participants over a period of time (often many years). Specifically, cohort studies recruit and follow
participants who share a common characteristic, such as a particular occupation or demographic similarity.
• Intervention Studies: Intervention (or Experimental) studies differ from observational studies in that the
investigator assigns the exposure. They are used to determine the effectiveness of an intervention or
the effectiveness of a health service delivery.

DATA COLLECTION METHODS
The choice of method is influenced by the data collection strategy, the type of variable, the accuracy required,
the collection point and the skill of the enumerator. Links between a variable, its source and practical methods for
its collection can help in choosing appropriate methods. The main data collection methods are:
1. Registration: registers and licenses are particularly valuable for complete enumeration, but are limited to
variables that change slowly, such as numbers of fishing vessels and their characteristics.
2. Questionnaires: forms which are completed and returned by respondents. An inexpensive method that is
useful where literacy rates are high and respondents are co-operative.
3. Interviews: forms which are completed through an interview with the respondent. More expensive than
questionnaires, but they are better for more complex questions, low literacy or less co-operation.
4. Direct observations: making direct measurements is the most accurate method for many variables, such as
catch, but is often expensive. Many methods, such as observer programmes, are limited to industrial
fisheries.
5. Reporting: the main alternative to making direct measurements is to require fishers and others to report
their activities. Reporting requires literacy and co-operation, but can be backed up by a legal requirement
and direct measurements.

Ethical issues in epidemiologic research and public
health practice
The results of epidemiologic research studies contribute to generalizable knowledge by elucidating the
causes of disease; by combining epidemiologic data with information from other disciplines such as genetics
and microbiology; by evaluating the consistency of epidemiologic data with etiological hypotheses; and by
providing the basis for developing and evaluating health promotion and prevention procedures
The primary professional roles of epidemiology are the design and conduct of scientific research and the
public health application of scientific knowledge. This includes reporting research results and maintaining and
promoting health in communities. In carrying out these professional roles, epidemiologists often encounter a
number of ethical issues and concerns that require careful consideration
Specific ethical issues arising in epidemiologic research and public health practice that have been highlighted
in ethics guidelines include minimizing risks and providing benefits, informed consent, avoiding and disclosing
conflicts of interest, obligations to communities, and the institutional review board system

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