1. Dr. Khem R. Sharma, Assistant Professor
School of Public Health & Community Medicine, BPKIHS
2. To describe the burden of disease or prevalence of risk
factors, health behaviors, or other characteristics of a
population that influences the risk of disease
To determine the causes or risk factors for illness
To determine the relative effectiveness of interventions
3. Medical Research methods include scientific ways to
distinguish facts from fiction in broadly two categories:
1) Quantitative research methods: emphasize objective
measurements (numerical data) and analysis of poll,
questionnaire data or manipulating pre-existing
statistical data using different computational
2) Qualitative research methods: focused more on
discovering underlying meanings and patterns of
relationships in a manner, that does not involve
mathematical models. Example: Focus Group
4. Quantitative research is a systematic investigation of
assembling quantifiable data and performing statistical,
mathematical or computational techniques to present it.
The goal in conducting quantitative research study is to
determine the relationship of one entity [independent variable]
with another [dependent or outcome variable] within a
Quantitative research designs are either descriptive [subjects
usually measured once & establishes only associations between
variables] or experimental [subjects measured before and after
a treatment & establishes causality].
5. Structured tools: Questionnaires are used to gather quantitative
data which helps in collecting in-depth and accurate information
from the survey respondents.
Sample size: Quantitative research is conducted based on
significant sample size that represents the target population, with
the use of appropriate sampling methods to meet the research
Prior studies and preparation: Adequate groundwork needs to be
done before starting the study as all aspects of the study needs to be
carefully designed before data collection ensues.
6. Quantitative data: in the form of numbers and statistics
represented by tables, charts, graphs etc. makes it easy to
understand the information
Generalization of results: Results of the research can be generalized
to a subgroup or even the entire population to take appropriate
actions for improvement.
The study can usually be replicated or repeated, given its high
7. Quantitative methods have an objective approach to studying
research problems as a consequence, the results of quantitative
research may be statistically significant but may be humanly
insignificant.( Biologically not plausible)
Though more efficient and able to test hypotheses, it may miss
Uses a static and rigid approach and so employs an inflexible
process of discovery;
Results provide less detail on behavior, attitudes, and
8. I. Observational Studies
a) Descriptive (case study, case series, cross-sectional)
b) Analytical (cross-sectional, case-control, cohort ,
II. Experimental Studies
a) Randomized Control Trial (RCT/ Clinical Trials)
b) Field Trials (Healthy people as units)
c) Community trials (Communities as units of study)
9. Observational studies allows nature to take its own
course; the investigator keeps measuring, but does not
Descriptive studies are limited to description of the
problem that exists in that population
Analytical studies go one step further and analyses the
relation between the outcome variable and various factors
implicated in its occurrence.
Experimental/Intervention studies involve active
interventions to change the progression of a disease/event.
10. The first phase of an epidemiological investigation concerned
with observing the distribution of disease or health-related
characteristics in human populations & identifying the factor
with which the disease seems to be associated.
Such studies basically ask the questions.
a) When is the disease occurring ? - time distribution
b) Where is it occurring ? - place distribution
c) Who is getting the disease? - person
11. Analytical Studies
interest is the individual within
to test hypothesis
inference is not to individuals.
but to the population from
which they are selected.
Answer why and how
• look at entire populations
• to formulate hypothesis
• gives person, time & place
status of Health Problems
• Answer what, who, where,
12. Simplest form of an observational study
Based on a single examination of a cross-section of
population at one point in time - the results of which can be
projected on the whole population (Photograph)
Usually Descriptive-Analytical when two groups are
Provides very little information about the natural history of
disease or about the rate of occurrence of new cases
13. Common first approach to test causal hypothesis
Three distinct features:
a) Both exposure & outcome have occurred before the start of
b) Study proceeds backwards from effect(outcome) to cause
c) Uses a control/ comparision group to support or refute an
To study rare diseases
To study multiple exposures that may be related to a single
15. 1) Selection of cases and controls: suitable controls may present
Sources: Case(hospital/gen population)
Controls- (hospital/relatives/neighbor hood/gen popn)
2) Matching to ensure comparability between cases and control but
controls should free from the disease under study.
Process by which controls are selected such that they are similar to
cases with regard to certain pertinent selected variables (e.g., age,
gender etc) which are known to influence the outcome of disease and
which if not adequately matched for comparability, could confound
the results (eg: Alcohol in esophageal cancer VS cig).
16. 3) Measurement of exposure: Definitions and criteria of exposure
should be the same and information about exposure should be
obtained in precisely the same manner for both cases and
obtained by interviews/questionnaires or studying past hospital,
employment records etc. of cases
4) Analysis: to find out-
a) Exposure rates among cases & controls to the suspected factor +
b) Estimation of disease risk associated with exposure (Odds
17. Measure of the strength of the association between risk factor and outcome.
cross product of the 2 X 2 table
Odds ratio is based on three assumptions:
1) the disease being investigated must be relatively rare
2) the cases must be representative of those with the disease, &
3) The controls must be representative of those without the disease.
If a race horse runs 100 races and wins 25 times and loses the rest, the
probability of winning is 25/100 = 0.25 or 25%, but the odds of the horse
winning are 25/75 = 0.333 or 1 win to 3 loses.
18. What is a cohort?
-Well-defined group of people who share a common
characteristic or experience within a defined time period
(e.g., age, occupation, exposure to a drug or vaccine,
Example: Those born in 1990 form the birth cohort of
What are other examples of cohorts?
19. Longitudinal study, follow-up study
Participants classified according to exposure status and
followed-up over time to ascertain outcome
Can be used to find multiple outcomes from a single exposure
Appropriate for rare exposures or defined cohorts
Ensures temporality (exposure occurs before observed
21. COHORT STUDY
The distinguishing features of cohort studies are :
1) the cohorts are identified prior to the appearance of the
disease under investigation
2) the defined study groups are observed over a period of
time to determine the frequency of disease among them
3) the study proceeds forward from cause to effect.
22. 1) when there is good evidence of an association between exposure
and disease as derived from clinical observations and supported
by descriptive and case control studies
2) when exposure is rare but the incidence of disease high among
exposed. (eg: hirosima nuclear disaster/Bhopal gas)
3) To learn about multiple outcomes due to a single exposure (eg:
Health effects of a nuclear power plant accident)
4) when attrition of study population can be minimized e.g., follow-
up is easy, cohort is stable, cooperative and easily accessible
5) when ample funds are available.
23. Three types of cohort studies have been distinguished on the basis of the
time of occurrence of disease in relation to the time at which the
investigation is initiated and continued :
1) Prospective cohort studies: Eg - Doll & Hill, Framingham Heart Study
2) Retrospective cohort studies: Eg: study of lung cancer in uranium
3) Combination of retrospective and prospective cohort studies:
The cohort is identified from past records, assessed to date for the
outcome and the same cohort is followed up prospectively into future for
further assessment of outcome.
24. It is a direct measure (or index) of the "strength" of the
association between suspected cause and effect.
A RR of one indicates no association while RR of 2 indicates
that the incidence rate of disease is 2 times higher in the
exposed group as compared with the unexposed
RR = Incidence of disease (or death) among exposed
Incidence of disease (or death) among non-exposed
25. The difference in incidence rates of disease (or death)
between an exposed group and non-exposed group expressed
as a percentage.
Attributable risk indicates to what extent the disease under
study can be attributed to the exposure
Population Attributable Risk (PAR) provides an estimate of
the amount by which the disease could be reduced in that
population if the suspected factor was eliminated or modified.
26. Experimental research studies compare the effectiveness
of medical treatments, management & prevention
strategies, and other medical or public health
Design is very similar to that of a prospective cohort
study- intervention is present.
Investigator assigns the exposure status in clinical trials,
while subjects' genetics, behaviors, and life circumstances
determine their exposures in a cohort study