3. DEFINATION OF EPIDEMIOLOGY
• The word “epidemiology” is derived from the
Greek word :-
Epi = “amongst/upon”
• demos = “people”
• logos = “ study”
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4. - Epidemiology is the basic science of preventive and social
science
- It is the study of pattern ,causes and effect of health and
disease conditions in a defined population.
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5. - Greek physician Hipocretes,father of medicine,was the first
Epidemiologist. (460 – 375 BC)
- Distinguished between epidemic diseases and endemic
diseases.
- advocated that environmental factors can influence
occurrence of disease.
• - Foundation of epidemiology laid in the 19th century.
• - Evolved rapidly over the last 3 decades.
• - Early 20th century mathematical methods were introduced
• statistical support.
eg. Fluoridation reduced dental caries.
Ceasation of tobacco smoking,linked to lung cancer
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HISTORY OF EPIDEMIOLOGY
6. EVOLUTION OF MODERN EPIDEMIOLOGY
• Modern epidemiology has entered the most exciting
phase of its evolution.
• By identifying the risk factors of chronic
diseases,evaluating treatment modalities and health
services,it has provided new opportunities for
prevention ,treatment ,planning and improving the
effectiveness health services.
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7. Definition - Epidemiology
• Epidemiology is the study of the distribution
and determinants of health-related states or
events in specified populations, and the
application of this study to the control of
health problems.
• Last JM (ed) (1988). A dictionary of epidemiology. New York: Oxford University Press
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8. Distribution
Epidemiology is concerned with the frequency and pattern of
health events in a population.
Frequency: number of such events in a population and rate or
risk of disease in the population.
Pattern: occurrence of health-related events by time, place, and
personal characteristics.
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9. Determinants
Epidemiology is also used to search for causes and other factors that
influence the occurrence of health-related events.
Determinants includes factors that influence health:
biological,chemical,physical,social,cultural,econonmic,
genetic and behavioural.
Analytic epidemiology attempts to provide the Why and How of such events
by comparing groups with different rates of disease occurrence and with
differences in demographic characteristics, genetic or immunologic make-
up, behaviors, environmental exposures, and other so-called potential risk
factors.
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10. Health-related states or events
Originally, epidemiology was concerned with epidemics (rapid spread) of
communicable diseases.
Then epidemiology was extended to endemic (Constantly present)
communicable diseases
• and non-communicable infectious diseases.
More recently, epidemiologic methods have been applied to chronic diseases,
injuries, birth defects, maternal-child health, occupational health, and
environmental health.
In these lessons we use the term “disease” to refer to the range of health-
related states or events.
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11. EPIDEMIOLOGY & CLINICAL MEDICINE
•
• Epidemiology Clinical Medicine
1. The unit of study is a defined 1. The unit of study is a case or
• population or population at risk. or cases.
• 2. Study the disease pattern in the 2. Often concerned with those who
entire population-sick & healthy. are sick.
3. Identify the source of infection, 3. Diagnosis ,prognosis,specific
mode of spread,future trend, treatment.
and control measures.
4. Investigator goes to the community 4. Patient comes to the doctor.
5. Subject matter is ‘conceptual’ 5. Easily peceived.
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12. AIMS OF EPIDEMIOLOGY
- Initially,epidemiologic practice was limited to detection and control of
communicable diseases.
- Now, used to study maternal & child health, family planning,
mental health, nutritional disorders, accidents, & life style & its effect on
health
The International Epidemiological Association 3 main aims of epidemiology:-
1. To describe the size and distribution of the disease problems inhuman
population.
2. to provide data essential for planning ,implementation, & evaluation of
health services for the prevention,control & treatment of diseases
3. To identify aetiological factors, risk factors, in the pathogenesis of disease.
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13. Uses Of Epidemiology (Morris)
1. To study historically the rise & fall of disease
in the population.
- To study the history of disease pattern in
human population.
- To study disease profiles & time trend in
human population
- Study of these trends we can make useful
projections into the future & identify
emerging health problems.
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14. Population or community health assessment
(2)
To set policy and plan programs, public health officials must assess the health of
the population or community they serve and must determine whether health
services are available, accessible, effective, and efficient.
To do this, they must find answers to many questions:
What are the actual and potential health problems in the community?
Where are they?
Who is at risk?
Which problems are declining over time?
Which ones are increasing or have the potential to increase?
How do these patterns relate to the level and distribution of services
available?
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15. 3. Individual Decisions
People may not realize that they use epidemiologic
information in their daily decisions.
When they decide to stop smoking, take the stairs
instead of the elevator, order a salad instead of a
cheeseburger with French fries, or choose one
method of contraception instead of another, they
may be influenced, consciously or unconsciously,
by epidemiologists’ assessment of risk.
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16. 4. Completing the clinical picture
(Natural History of disease)
When studying a disease outbreak, epidemiologists depend on
clinical physicians and laboratory scientists for the proper
diagnosis of individual patients.
But epidemiologists also contribute to physicians’ understanding
of the clinical picture and natural history of disease.
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17. 5. Search for causes & risk factors
Much of epidemiologic research is devoted to a
search for causes, factors which influence
one’s risk of disease.
Epidemiology often provides enough
information to support effective action
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18. 6.PLANNING & EVALUATION OF INTERVENTION
Epidemiology is involved in evaluating the
effectiveness and efficiency of health services
or health care intervention or drug therapy.
Developing appropriate technology for treating
disease and increase affordability of the
services.
Essential for the rational allocation of the limited
resources.
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19. 7. COMMUNITY DIAGNOSIS
• - Identification and quantification of health problems-
• mortality, morbidity rates & ratios.
• - By quantification we are laying down priorities in disease control &
prevention.
• - serves as a bench mark for the evaluation of health services
• at a later date.
• - Quantification of health problems can be a source of new knowledge
about disease distribution, causation and
• prevention.
• - Epidemiology therefore has been described as a “diagnostic
• tool” of community medicine.
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20. Types of epidemiological studies
Observational study
Descriptive
• Case reports and case series
• Cross sectional studies
• Ecological studies
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Analytic studies
• Cohort study
• Prospective
• Retrospective
• Case control study
Interventional study
Randomized controlled trial/
• Clinical trial
Field trial/ Community trial
21. A. Descriptive Epidemiology
Is concerned with understanding and describing the patterns of disease and
illness in human populations in order to obtain clues to the possible
etiology of disease.
Every disease or health event you will encounter in dentistry has a natural
history, i.e. a signature pattern that occurs time and again in the absence
of any outside intervention.
This pattern often provides clues as to causes
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22. a. DESCRIPTIVE
- Describes pattern of disease
- Risk factors
- Determinants of health
- WHO WHICH WHEN WHERE
- Two types
- Ecological - Cross sectional
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23. CROSS-SECTIONAL STUDIES
- Measures prevalence of disease
- Measures exposure and effect same time
- Not easy to assess reasons for association
- Know whether exposure precedes or follows effect
- First step of investigation of cause
- Surveys and questionnaires
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24. B. ANALYTICAL
• Tests hypothesis
• Tests casual role of disease
• What Why How
• Strength and correlation
• Evaluation of intervention
• Case – control study (retrospective)
• Cohort study (prospective)
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25. b. COHORT STUDIES
• Follow – up or incidence studies
• Group of people (a cohort)
• Free of disease
• Longitudinal study data collected more times
• Best info causation of disease
• Most direct measure of disease
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26. c. CASE CONTROL STUDIES
• Investigate cause of disease
• Rare Disease
• Data more than one point of time
• Longitudinal
• Also called “retrospective”
• Begins selection of cases
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27. C. INTERVENTIONAL STUDIES
a. Randomized Control Trial (RCT)
-
- Epidemiological experiment
- Study preventive or therapeutic regimen
- Subjects randomly allocated
- Results of outcome compared
- Results unaffected by selection biases
- Value of new therapies.
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28. b. FIELD TRIALS
• Involve disease free people
• But presumed to be at risk
• Data collection in the field
• Often huge undertakings
• Preventive program vaccines
• Used to evaluate interventions aimed at
reducing exposure
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29. c. COMMUNITY TRIALS
• Treatment groups are communities
• Disease : social origin
• Intervention diverted to group behavior as
well as individuals.
• Only small number of communit
•
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