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
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
25.
26.
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
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.
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
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
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
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-
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.
