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General Epidemiology
1. Principles of Epidemiology
Dr. Akhilesh Bhargava
MD, DHA, PGDHRM
Prof. Community Medicine
&
Director-SIHFW, Jaipur
2. Epidemiology
The study of distribution and
determinants of health problems in
specified populations and the application
of this study to the control of these
problems. It is the scientific method of
problem solving used by "disease
detectives"--epidemiologists, laboratory
scientists, statisticians, physicians and
other health care providers, and public
health professionals--to get to the root of
health problems in a community.
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Akhilesh Bhargava
3. Epidemiology
Define ?
vA study of all diseases/health events
Øinfectious/non-infectious
Øacute/chronic
Øcommunicable/non-communicable.
vScience of rates expressed as
probability
v“ Anything that happens to people”
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4. Epidemiology:
Gen. Objectives
• Explaining the Causal mechanism of
disease and process of deviation in
Health.
• Explaining the reason for Local disease
occurrence.
• Effective planning and administration of
Health Care Services.
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5. Specific Objectives
1. Understanding causation of disease
with specific purpose of--
ØFormulation and selection/rejection
of hypothesis.
ØTesting hypothesis through
*Survey
*Observation studies
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6. Specific Objectives…
2. Testing validity of rationale of
control /intervention programs
3. Classify disease/disability based
on :
Distribution
Causal factors, and
Natural history of disease
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7. Specific Objectives
4. Explaining local disease pattern
5. Administrative Guidance
– In assessing Need, Utilization &
Effectiveness
– In monitoring & evaluation of control
programs (cost effectiveness & cost benefit
analysis)
– In Logical Planning of
• Services
• Resources
• Programs
• Reach &
• Risk Approach
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8. Planning: Terms
• Planning-“an act or process of
choosing between alternatives to
accomplish preset goals”.
• Plan denotes a blue print of action
• Program is a strategy with defined
Objectives.
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9. Goal:
• The proposed long-range benefits of
the program for a specified area,
defined in general terms. A goal is the
ultimate objective; for example,
“reducing the incidence of HIV in (a
country).”
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10. Purpose:
• The overall objective (also called
strategic objective) of the program, for
example, “to increase the accessibility
to and use of palliative care facilities in
(a particular geographic area).”
• ultimate measure of the program’s
effectiveness.
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11. Objectives:
• The anticipated outcomes or benefits that
are the expected results of implementing
a strategy. They are described in
measurable terms and indicate a specific
period of time during which these results
will be achieved.
• Should be SMART
• specific,
• measurable,
• appropriate,
• realistic, and
• time-bound
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12. Strategy
• A strategy is a plan (to choose) to
achieve a particular goal or result;
and reveals the logic of your
choices.
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13. Approach:
A statement that describes how the
program will achieve its objective. That
is, activities that will help the program
achieve its objectives most effectively
and feasibly.
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14. Monitoring
• A methodological arm of evaluation that
tracks the program’s incremental steps to
its effect and informs the final evaluation
report.
• A continual, routine effort requiring data
gathering, analysis, and reporting on
results at periodic intervals
• Periodic, regular
• Focuses on inputs, outputs, process
outcomes, work plans
• Basic purpose is improve efficiency
and adjust work plan
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15. Evaluation
• A technical activity that measures the
program’s impact and effectiveness
as a whole.
• Is not about assigning a “grade” of
success or failure at the end of a
project.
• Episodic
• Focuses on effectiveness, relevance,
impact, cost-effectiveness
• Basic purpose - improve
effectiveness, impact, and future
programming
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17. Epidemiology?
“Study of distribution and
determinants of health related
state or events & disease in human
population”
“Science of rates expressed as
probability”
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18. Uses of Epidemiology
• Describe Health events
• Identify the cause of disease
• Identify the Risk factors
• Describe clinical pattern of disease and
identify syndromes
• Identify effective control and/or
preventive measures
• Risk Approach
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19. Uses of Epidemiology
• Take suitable administrative measures in-
• Assessing Need, Utilization &
Effectiveness
• Monitoring & evaluation of control
programs (cost effectiveness & cost
benefit analysis)
• Logical Planning of
» Services
» Resources
» Programs
» Reach &
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21. Epi. Studies- Types
Study Alternative Name Unit of Study
Observational
Descriptive
Analytical
Ecological Correlation Population
Cross sectional Prevalence Individuals
case control Case reference individuals
cohort follow-up individuals
Experimental Intervention
Randomized Clinical trial Patients
field trials Healthy people
Community trials Community intervention community
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22. Descriptive Epidemiology?
Study of distribution of a disease in a
population, and observing the basic
features of its distribution in terms of
time, place, and person.
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23. Descriptive Epidemiology:
Objectives
• To evaluate trends and allow comparison
among different population groups
• To provide basis for planning, provision
and evaluation of services
• To identify problems to be studied by
analytical methods
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24. Descriptive Epidemiology
describes-
• Who gets sick and who does not
• Where Rates are highest and lowest
• Temporal pattern of Disease
• Seasonality
• Secular trends decided by changes in-
• Diagnostic techniques
• Denominator data
• Age distribution of population
• Survival
• Actual incidence
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25. Reasons for changes in Trends:
Real
• Changes in Age distribution of
population
• Changes in Survival pattern
• Changes in Actual incidence for
• Genetic
• Environmental factors
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26. Reasons for changes in Trends:
Artifactual
• Errors in Numerator due to-
• Changes in disease recognition
• Change in classification of cause
• Change in classification codes of cause of
death
• Changes in accuracy of reporting age at
death
• Errors in denominator due to errors of
enumeration
• ICD-10 has 8000 categories as
compared to 4000 in ICD-9
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27. Descriptive Epidemiology
Descriptive epidemiological approach
attempts to describe the disease in
terms of its attributes & variables and
answers the questions like-
• Who (Person)
• Where (Place)
• When (Time)
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29. Who (Person) ?
Is getting the disease
Attributes & Variables
• Age
• Sex
• Ethnicity
• Marital status
• Occupation
• Education
• Income group…………
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30. Age
Malnutrition
Measles
STI
Arthritis/ Cancer
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31. Sex
Deaths per 100000 population from CAD
800
Deaths per 100000
700
600
500 Men
400
300 Women
200
100
0
Age groups 5-14 15-24 25-34 35-44 45-54 55-64
<1 1-4
Gap starts narrowing after 54
(menopause), suggests protective effect of estrogen
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32. Where (Place) ?
Where Rates are highest and
lowest
• Residence
• Occupation/ Work place
• At specific events
• Geographic sites
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33. Time (When) ?
Reflects on trend
• Year
• Season
• Day
• Date of Onset
• Duration
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34. Time trends
• Secular (Changes that occur over
long periods of time)
• Periodic (short term)
• Cyclic (Seasonal)
• Epidemic
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35. Secular trend is influenced by:
• Changes in completeness of source of data
• Changes in diagnostic ability
• Experience
• Techniques
• Changes in data classification approach
(ICD-9 to ICD-10)
• Demographic changes in population
• Changes in environment other than that
which is related to disease
• Changes in clinical
concepts, Diagnosis, Terminology
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36. Cyclic (Seasonal) trends
Changes in frequency over: Days, Weeks, Months, Years
Seasonal trend-Malaria & Pf cases, 1994 Rajasthan
80
Jan
70 Feb
60 Mar
Apr
50
May
% 40 Jun
30 July
August
20
Sep.
10 Oct.
0 Nov.
Pf cases Malaria Cases Dec.
Months
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37. Periodic (short term)
• Changes that occur in hours/
days / weeks
• Simultaneous exposure to
single source (Point source)
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• John Snow- Cholera
10
No. of cases
8
Cases
6
4
2
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Time 37
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39. Let us make an educated guess:
Hypotheses
• Why some people get the disease and
others do not
• Why disease occurs in some places
and not others
• Why disease occurs at some time and
not at others
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40. Developing Hypotheses
• Interrogate usual suspects!
• Source of agent
• Mode of transmission
• Usual reservoirs
• Known risk factors
• Exposures that caused disease
• Look at person, place and time for
clues
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41. Developing a hypotheses
• Requires familiarity with disease
• Hypothesis should be testable
• Still clueless?
• Talk with cases again
• Visit cases in their own situation
• Don’t forget outliers
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