Epidemiology is the study of the distribution and determinants of health-related states or events in populations and the application of this study to control health problems. The goals of epidemiology are to describe the magnitude of health problems, identify risk factors, and provide data to plan, implement, and evaluate health services. Epidemiologists use various tools like rates, ratios, and proportions to measure factors like mortality, morbidity, and environmental exposures. Descriptive epidemiology involves defining populations, diseases, and distributions by time, place, and person to form hypotheses about disease etiology, while analytical studies like case-control and cohort studies aim to determine associations between risk factors and diseases.

1. Epi-demio-logy
Dr Pallavi Potdar
Associate Prof.,
Community Medicine
D.Y. Patil Medical College Kolhapur

2. • What are the health problems in your
area?
• Where are they?
• Which problems are declining over time?
• Which are increasing?

3. John snow- London 19th
century

4. John snow- London 19th
century

8. Definition
• Study of distribution & determinants of health
related states or events in specified populations,
& the application of this study to the control of
health problems.

9. AIMS
• To describe distribution & magnitude of health problems
• To identify risk factors
• To provide data essential for
-planning,implementation,evaluation of services

10. Uses
• To study historically the rise & fall of disease in population
• Community diagnosis
• Planning & evaluation
• Evaluation of individuals risk & chances
• Syndrome identification
• Completing natural history of disease
• Searching for causes & risk factors

11. Tools of measurement
• Rates- death rate
• Ratios- sex ratio
• Proportions – no.of malnourished children x 100
total no. of children

12. Measurements in epidemiology
• Mortality
• Morbidity
• Disability
• Natality
• Environmental factors suspected of causing
disease
• Health care facilities

13. Mortality rates
no of deaths during yr.
1) Crude death rate=------------------------------x 1000
mid yr population
2) Specific death rates- due to TB ,age specific, sex
specific
3) Case fatality rate- total no of deaths due to particular disease x100
total no of cases due to same disease

14. Mortality rates
No of deaths from specific disease in a yr.
4)proportional mortality rate=------------------------------x100
• Total deaths from all causes
5) survival rate=total no of patients alive after 5 yrs./ total no of
patients diagnosed x 100

15. Morbidity
• Sickness/ illness
• Incidence-
• Prevalence

18. • prevalence= incidence x duration of disease

20. Exercise
• Duration of disease- 5 years
• 10 new cases per year
• Prevalence?

21. Epidemiologic methods
• 1) observational studies-
a) descriptive studies
b) analytical studies-
-ecological
-cross sectional
-case control
-cohort study

22. • 2) experimental studies-
randomised controlled trials
field trials
community trials

23. Descriptive epidemiology
• Defining the population to be studied
• Defining the disease under study
• Describing disease by time,place,person.
• Measurement of disease
• Comparing with known indices
• Formulation of aetiological hypothesis

24. Descriptive epidemiology
• Time distribution- week, month, day, year
1) Short term fluctuation-epidemic
2) Periodic fluctuation- seasonal trend,
cyclic trend- e.g. influenza
3) Long term fluctuation

27. Descriptive epidemiology…..
• Place distribution- urban, rural
- national/ international
• Person distribution- age, sex, occupation,
marital status

28. Analytical study
• Case control study
• Cohort study
• To determine if there is association
between risk factor & disease
• Strenth of association.

29. Case control study
• Comparison studies
• Confounding factors
• Basic steps-
• selection of cases & controls
• Matching
• Measurment of exposure
• Analysis & interpretation

30. Selection of cases-
1) definition of case- a)diagnostic criteria
b)eligibility criteria-only
newly diagnosed cases selected.
Sources of cases-
selection of controls-
1) must be free from disease under study. not
been exposed to risk factor.

31. • Selection of controls-
• Matching-
process by which we select controls in such a
way that they are similar to cases with regard to
certain pertinent selected variables which are
known to influence outcome of disease & which
if not adequately matched 4 comparability could
confound results.

32. 3)measurement of exposure-
By questionnaire,by interviews,from
hospital records,employment records.
4 ) Analysis-exposure rates,estimate
disease risk

33. Framework of case control study
Risk factors cases controls
present a b
absent
total
c
a+c
d
b+d

34. smokers
Cases
33
Controls
55
Non-smokers 2 27
Total 35 82

35. 1)Exposure rates =
Among cases = a/(a+c) =33/35=94.2%
Controls = b/(b+d) =
2)Estimation of risk –
Relative risk = incidence among exposed
incidence among non-
exposed

36. Cohort study
• Observational study
• Prospective / longitudinal / incidence/
forward looking study.
• Cause to effect
• Group of people sharing common
characteristic /experience within defined
period.

37. Cohort
Exposed to
risk factor
diseased
a
not
diseased
b
Total
a+b
Not
exposed
c d c+d

38. Cohort study…
Types-
•Prospective
•Retrospective
•Combination of prospective &retrospective

39. Elements of cohort study-
• Selection of study subjects
• Obtaining data on exposure
• Selection of comparison group
• Follow-up
• analysis

40. Advantages of cohort study
• Incidence can be calculated
• Association of 1 suspected factor to
several diseases can be studied
• Relative risk can be calculated
• Dose-response ratios

41. Disadvantages
• Large no of people involved
• Unsuitable for rare diseases
• Takes long time to complete study
• Expensive

42. Experimental epidemiology
• Randomized controlled trials
• Non-randomized controlled trials

43. Randomized controlled trial
Basic steps-
1)Drawing protocol
2)Selection of reference population
3)Randomization-experimental,control gr.
4)Intervention
5)Followup
6)Assessment of outcome
7)reporting

44. Drawing protocol
• Aims & objectives
• Selection of study gr. & control gr.
• Sample size
• Methodology

45. Criteria 4 study/reference gr.
• Representative of population
• Must give informed consent
• Susceptible to disease

46. Bias
• Subject variation
• Observer bias
• Bias in evaluation

47. • Single blind trial
• Double blind trial
• Triple blind trial

48. RCT types
• Clinical trials
• Preventive trials
• Risk factor trials
• Cessation exp
• Trial of aetiological agents
• Evaluation of health services-DOTS

49. NON-RANDOMIZED..
• Ethical,administrative reasons
• Cost
• Low incidence/prevalence-
• Less validity.

50. Association & causation
• Def- concurence of two variables more
often than would be expected by chance.
1)spurious association
2)indirect association
3)direct (causal) -----------a)one to one
b)multifactorial

51. Spurious association
• None actually associated.

52. Indirect association
• Confounding factors-

53. Direct association
• One to one
• Multi-factorial
Temporal association-does causal factor
exposure preceded disease?

54. Uses of epidemiology
• To study historically rise & fall of disease.
• Community diagnosis
• Planning, evaluation
• Evaluation of individuals risks, chances
• Syndrome identification
• Completing the natural history of disease
• Searching for causes, risk factors.

55. Infectious disease epidemiology
• Infection-the entry, development or
multiplication of infectious agent in body.
• Contamination-
• Infestation-
• Host-

56. • Epidemic-
• Endemic-
• Sporadic-
• Pandemic-
• Exotic-

57. • Zoonosis

58. Epidemic
• Unusual occurrence in the community or
region of disease ,specific health related
behaviour or other health related events
clearly in excess of expected occurrence.