Epidemiology is the study of disease patterns in populations. It involves describing disease occurrence, identifying risk factors, and applying findings to disease control. Descriptive epidemiology involves defining the population and disease, then describing disease characteristics by time, place, and person. Analytical epidemiology involves observational studies like case-control and cohort studies to identify risk factors and test hypotheses. Experimental epidemiology uses randomized controlled trials to test interventions and evaluate disease prevention measures. The goal of epidemiology is to control health problems in populations.

1. Epidemiology
Swapnil salve
Msc first year
MTCN MGM college of nursing

2. Definition and meaning
• What is the meaning of epidemiology?
Epidemiology comes from greek word
Epi means among the people and demos means the people or
population
It is the study among or upon the people

3. Definition
Definitions are,
The study of the frequency, distribution and determinants of
health related states or events in specified population and
application of this study to control health problems.
-- (John M Last, 1988)

4. Approaches of epidemiology
• The epidemiological approach to problem of health and
disease is based on:-
• Asking questions
• Making comparison

5. Asking question approach
• Asking question
• In this, the researcher or epidemiologist ask variety of questions and
getting answers that arouses further question and answer.
• Questions such as magnitude, nature, extent, geographical
distribution and time when it occurs.
Ex. Of questions are,
• What are the actual and potential health problems and their
characteristics?
• Which problem have declined?
• Which population is at risk?
• Where are they in terms of place?

6. Making comparison
• This method is to make comparison and draw inference
(conclusion)
• Comparison may be
• Between different proportion
• Rural population with urban group population
• Between sub group of population
• Male with female group of population
• Comparison between various periods of observation
• Different seasons

7. Tools of measurement
• Tools of measurement is used to test the magnitude of
disease
• Rate
• Ration
• Proportion
What is rate?
Rate is the measure of occurance of some particular events in a
population during a given a period of time, death rate, birth rate
or accident rate.
Ex. Death rate = no of deaths in one year
mid year population * 1000

8. Tools of measurement
• Ratio
Ratio is the relation in size between two quantities.
It is expressed in the form of 1:1 or 1:600 (means of 1 WBC
relative to 600 RBC in body)
• Proportion
Proportion is a ratio which indicates the relation in magnitude a
part of the whole.
Ex. No of delinuetes / total no of juveniles * 100

9. Epidemiology methods
Epidemiological methods are applied to know,
• Disease etymology and risk factor
• Pattern of spread of infection
• Forming hypothesis
• For purpose of prevention
Methods are,
1. Observational studies
1. Descriptive study
2. Analytical study
2. Experimental study / Interventional study

10. Descriptive Study
• What is descriptive study?
• A descriptive study is defined as one group of subject is
studied without any comparison group for describing
outcomes in terms of its frequency and its distribution
according to selected variables related to time, place and
person.
• It find out
• When disease occur
• Where it occurs
• Who is affected by disease

11. Procedure of descriptive
epidemiology
• Defining the population to be studied
• Defining the disease under study
• Describing the disease by
• Time
• Place
• Person
• Measurement of disease
• Comparing with known indices
• Formulation of an etiological hypothesis

12. Define population
• It may be whole population or sample from geographical area
• Population should be large enough
• Community should stable (without any migration)
• It should clear who belong and who does not belong to
population
Define disease under study
• Define the disease is important concern, if not clear then it is
source of error in study.
• Ex. Tonsillitis defined as clinically as infection caused by
streptococcus pyogenes

13. Describing disease
• Describe disease by,
• Time :- year, season, week, day, hour of onset
• Place :- duration, climatic zone, country, region, urban and rural
community, town, city
• Person:- Age, sex, marital status, occupation, education, birth
order, blood pressure, personal habits
Measurement of disease
The disease is measured as morbidity rates in two aspects,
incidence rate (occurance rate) and prevalence rate

14. Compare with known indices
• in this step, comparison between different population
(subgroup of same population)
• To find etiology and risk groups in population
Formation of etiological
hypothesis
Hypothesis is a supposition , arrived at from observation or
reflection.
It should clearly state, population, specific cause, expected
outcome, dose response relationship and time response
relationship.

15. Analytical study
• In analytical study, the subject of interest is individual and
inference is not individual, but to the population from which it
is selected.
• There are major two types,
• Case control study
• Cohort study
• Case control study
• Case control study is used to identify factors that contribute to a
medical condition, by comparing people with that condition
(cases) with patients who do not have the condition.

16. Case control study
• Basic steps are,
1. Selection of cases and controls
Cases should be newly diagnosed in specific period of time than old
cases or in advance stages of disease.
2. Matching
3. Measurement of exposure
It is done by interviews, by questionnaire or studying past records
of cases such as hospital records.
4. Analysis and interpretation
To find out exposure rate in population

17. Case control study
Advantages
• Easy to carry out
• Rapid and inexpensive
• No risk to subject
• No attention required
Disadvantages
• Problems of bias relies
on memory
• Accuracy issues
• Selection of appropriate
is sometime impossible

18. Cohort study
• Cohort is another type of analytical study which is usually
undertaken to obtain additional evidence to support the
existence of an association between suspected cause and
disease.
Indication
• When there is good evidence of exposure of disease
• When incidence rate of disease is higher among exposed

19. Experimental epidemiology
Experimental epidemiology is used to test the hypothesis.
In this investigator controls one factor, independent variale and
measure the subsequent effect on dependent variables.
Ex.
a) Test the effectiveness of a drug or treatment (therapeutic
trial)
b) To know the efficacy of a preventive measure or procedure
c) To determine the effect of controlling risk factor for a given
disorder (intervention trial) on the individual subject

20. Randomized control trial
1. To provide scientific proof of etiological (risk factor)
2. To provide a method of measuring the effectiveness of
health services for the prevention, control and treatment of
disease and improve the health of the community
AIMS
1. Drawing up a protocol
2. Selecting experimental population
3. Randomization
4. Manipulation and intervention
5. Follow up
6. Assessment of outcome

21. 1. Establishing a probable diagnosis
• Establish diagnosis in clinical round
• Visit the affected area and collect relevant information
• Meet with doctors, patients
• Visit all affectd families and collect essential data
• Data of expected cases found from surveillance data,
clinicians, hospital registers, hospital investigation
2. Verify diagnosis
Comparison of data with previous records. The record should be
minimum of 3 years. Ex. Lab test, identification of the serotype
Steps of investigation

22. 1. Define the population at risk
• Prepare the map of the area
• Counting the population
• This is done by studying list of cases from name, age, sex,
address, date of onset of illness, signs and symptoms
2. Define and identify cases
A case definition is a standard set of criteria for decading
wheather an individual should be classified as having the health
condition of interest or not.
Steps of investigation

23. 1. Perform descriptive epidemiology
Categoriezed samples based on,
• Time :- onset, peak, incubation period, time of exposure.
• Place :- place of work, food places, area at risk
• Person :- distribution by age, gender, profession etc.
2. Develop hypothesis
Hyposthesis should address,
a. Source of the agent
b. Mode of transmission
c. Vector
d. Exposure that caused the disease
Steps of investigation

24. 7. Test the hypothesis
It is done by doing analytical study (case control and cohort
study) to conclude hypothesis.
8. Refine hypothesis and do additional studies
9. Write report and communicate findings
• Report writing involve,
• Introduction, background data, methods, results, discussion and
recommendation
• Report will use in future and serve as knowledge base of
epidemiology and public health
Steps of investigation

25. 7. Control and preventive measure
A. General measures
• Use of personal protective equipment by health care provider to
prevent infection
• Ex. Maintain hygien or cleanliness
B. Specific measure
• Agent :- removing source
• Environment
• Interupting transmission ex. Waterborn outbreak
• Access to safe drinking water and maintain hygienic
Steps of investigation

26. 1. Define epidemiology
2. Explain scope of epidemiology
3. Explain aim of epidemiology
4. Selection of epidemiological approach
5. Describe methods of epidemiology
6. Enlist tools of measurement
7. Define morbidity and mortality
8. Indicate measurement of morbidity
9. Describe and indicate measurement of mortality
Summary