This document discusses descriptive epidemiological studies. Descriptive studies are usually the first phase of an epidemiological investigation and are concerned with observing disease distribution and characteristics in populations. Key points: - Descriptive studies rely on pre-existing data and ask "who, where, when" to generate hypotheses. - An operational definition of the disease is needed for accurate identification and measurement in the target population. - The target population or "defined population" becomes the denominator for calculating disease rates.

1. DESCRIPTIVE STUDY
Dhanushree G
6th Term
SSIMS Davangere

2. EPIDEMIOLOGY
The Dynamic study of:
● Occurrence
● Distribution
● Determinants
of health and disease
in a population

3. So,,,, EPIDEMIOLOGY
● is the basic science of public health
● Provides insight about the nature , causes , and
extent of health and disease
● Provides information needed to plan and target
resources appropriately.

4. EPIDEMIOLOGIC
STUDY DESIGN

5. OBSERVATIONAL
STUDIES
● Descriptive studies
● Analytical studies
-Ecological
-Cross sectional
-Case control
-Cohort
EXPERIMENTAL
STUDIES
● Randomized control
trials
● Field trials
● Community trials

6. DESCRIPTIVE STUDY
❏ Descriptive studies are usually the first phase of
an epidemiological investigation.
❏ These studies are concerned with observing the
distribution of disease or health related characteristics
in human populations and identifying the
characteristics in which the disease is associated.

7. The study basically asks the following questions:

8. DESCRIPTIVE vs. ANALYTICAL
● Used when little is
known about the
disease
● Rely on pre existing
data
● Who,where,when?
● Gives an Hypothesis
● Used when insight
about various aspects
of disease is available
● Rely on development
of new data
● WHY?
● Tests the Hypothesis.

9. PROCEDURES IN DESCRIPTIVE
STUDIES
1. Defining the Population to be studied
2. Defining the Disease under study
3. Describing the disease by : Time , Place , Person
4. Measurement of disease
5. Comparing with known indices
6. Formulation of an aetiological Hypothesis.

10. 1. DEFINING THE POPULATION
➔ Investigations done on populations and
not on individual.
➔ Specify the type of population under
study.
➔ Define ‘Population Base’
➔ Defined population

11. CRITERIA :
➢ Large
➢ Stable
➢ Not different from other communities
➢ Community participation
➢ Accessibility of health services

12. The Population Base : Includes the total number and its
composition in terms of age,sex,occupation, and cultural
characters.
The Defined population can be whole population in a
geographic area or specially selected group like
age/sex/occupational groups,hospital patients,school
children,pregnant women etc.

13. For example,
To study the problem of MEASLES in a primary health
centre area, during a given year,
● The population under study is all under fives
● The area is the entire jurisdiction of PHC
● The time is the particular year

14. Thus,
The study population [Defined Population] :
● becomes the population at risk ,
● it becomes the denominator and
● helps in calculating the rates
● which is further used in measuring the disease
frequency.

15. 2. DEFINING THE DISEASE
The disease taken up for study has to be defined.
CLINICAL
DEFINITION
OPERATIONAL
DEFINITION

16. CLINICAL DEFINITION
➔ Given by clinician
➔ Serves to convey particular information
➔ But cannot be used to measure the disease in the
community.
➔ The Epidemiologist or the field workers may not be able to
identify those who have the disease from those who do not
accurately.

17. OPERATIONAL DEFINITION
➔ Accepted by Epidemiologists ,Observers,Field
workers.
➔ Operational Definition is a definition by which
the disease or condition can be identified and
measured in the defined population with a degree
of accuracy.

18. EXAMPLE (1) : TONSILLITIS
CLINICAL OPERATIONAL
Inflammation of tonsils
caused by infection
usually with Strept.
pyogenes
Enlarged red tonsils
with white exudate,
which on throat swab
culture shows
predominantly S.
pyogenes.

19. EXAMPLE (2) : LEPROSY
CLINICAL OPERATIONAL
Chronic infectious
systemic disease caused
by Mycobacterium leprae
Hypopigmented patches
with partial or total loss of
sensation,with thickening of
nerves and demonstration
of acid fast bacilli in skin
smear examination.

20. Hence,,
❏ Clinicians - do not need precise definition
❏ Epidemiologists - Need precise and valid definition.
❏ Diseases which do not have pathological signs and
symptoms, Epidemiologist frames his own
definition.

22. 1) Which of the following does descriptive
study cannot answer?
● WHO?
● WHEN?
● WHY?
● WHERE?

23. 2) Which of the following definition of disease does
an epidemiologist depend upon?
● Clinical definition
● Operational definition
● Surgical definition
● Simple definition

24. 3) We call Defined population as ‘Population at
Risk’ BECAUSE :
● It becomes the Denominator for calculating rates
● It becomes the Numerator for calculating rates
● It is chosen from the Population base
● It is large and stable.

25. 4) The study that tests the Hypothesis is:
● Descriptive Study
● Case series/reports
● Experimental study
● Analytical study

26. 5) Arrange the following steps of Descriptive study in the
correct order :
❏ Defining the Disease under study
❏ Measurement of the disease
❏ Formulating an aetiological hypothesis
❏ Defining the population to be studied
❏ Describing the disease wrt Time , Place , Person
❏ Comparing with the known indices.

27. THANK
YOU :)