This document provides an overview of common study designs used in public health research. It describes qualitative and quantitative study designs, as well as observational and experimental designs. For observational designs, it distinguishes between descriptive studies like case reports, cross-sectional and longitudinal studies, and analytical studies like case-control and cohort studies. Experimental designs actively modify a study variable through an intervention to examine outcomes between groups. The objectives are to help participants understand different study designs and choose appropriate designs according to their research questions.

1. Dr.A.P. Kulkarni
Professor & Head
Department of Community Medicine
Rural Medical College, LONI
OVERVIEW OF STUDY DESIGNS

2. Lesson objectives
At the end of the lesson, the participants will be
able to
Enlist the common study designs
Choose study design suitable for their RQ

3. Common study designs

4. Qualitativestudy
Finds out how and why an event/phenomenon occurred
and when did it occur
Does not answer questions like in how many families it
occurred, how many families/communities were
involved etc.)
Helps to do a rapid assessment of the situation
Helps understand human behaviour, culture, practices
Helps understand the anomie (anarchy, normlessness)
and conflict situation in human society

5. Qualitativestudy: Commonly used
methods
Ethnography (Taking notes)
Participatory (observer takes active part, action based
research)
Non-participatory (approach is similar to participatory
research, observer does not get involved in the affairs)

6. Quantitativestudy
Stress on quantification of answer to RQ
Quantifies frequency, difference, association, or correlation
May give answer to “why” and “how”
Use of statistics for describing the answer to RQ: Descriptive
statistics
Use of statistics for interpretation: Inferential statistics

7. Observational studies
Investigator
passive observer
No active attempt
to modify the
variable in RQ
Two types:
Descriptive and
Analytical
Descriptive study
Case report/ Case series
Cross sectional study
Longitudinal study

8. Descriptivestudies
Case Report/ Case series
Report of one or more rare
event/ events
Un-usual presentation of a
disease
Rare , hence not
generalisable
Cross sectional study
• RQ descriptive type
• No hypothesis
• No comparison group
• Observations of variable at
one point of time (Snap)
• Indicated for estimating
prevalence
• May be done on entire
population or sample

9. Descriptivestudies
Longitudinal study
• RQ descriptive type
• No hypothesis
• No comparison group
• Observations of variable at
more than one point of
time
• Indicated for estimating
incidence, time trends
• May be done on entire
population or sample
• Same sample each time or
different each time, but
same population
• Cross sectional studies at
different points
• Like a series of snap shots
taken at different times

10. Analytical studies
Case control study
• RQ difference type or
association type
• Hypothesis derived from
previous descriptive studies
• Two groups:
1. Those with outcome
[Dependent variable]
2. Those without outcome
Objective: To study
difference or association of
dependent variable with
one or more independent
[Predictor] variables
Outcome and independent
variable present before
study starts
Backward looking or
retrospective

11. Analytical studies
Cohort study
• RQ difference type or
association type
• Hypothesis derived from
previous descriptive studies
• Two groups:
1. Those with Independent
[Predictor] variable
2. Those without
Independent [Predictor]
variable
Objective: To study
difference or association of
independent variable with
one or more dependent
[outcome] variables
Independent variable
present before study starts
Dependent variable NOT
present at time of study
Forward looking or
prospective

12. Experimental studies
• RQ difference type or
association type
• Hypothesis derived from
previous studies
• Active attempt by
investigator to modify study
variable by way of
“Intervention
• Two or more groups
1. Given intervention
2. Not given intervention
under study [Control
group]
 Intervention: Giving /
Withdrawing
 Objectives:
1. To study association of
outcome with
intervention
2. To study difference in in
outcomes two groups

13. Evaluation of diagnostic test
• Variant of observational
study
• Objective to evaluate utility
of new test
• New test compared with
gold standard
• Hypothesis present

14. Variantsof Experimental studies
• Clinical trial: Placebo
controlled, No placebo
• Clinical trial: Parallel
groups, Cross over type
• Before- after trial
• Field trial
• Vaccine trial
Choice of Study Design
Type of RQ
Hypothesis
Objective

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