Study designs in epidemiology

1. Epidemiological Study
Designs
Dr Jazeela Mohamed Siddique
Senior resident
Department Of Community Medicine

2. Introduction
• Study designs directs how investigation is conducted
• methods used in research to gather the data needed to explore
a research question
Research
question
Study
design
Data
collection
Data
Analysis
Result
interpretation

3. Classification
Observational studies
Descriptive studies
Analytical studies
Experimental studies
Randomized controlled trials
Field trials
Community trials

4. Observational studies
• Careful observations
• Allow natural course of events
• Investigator measures but does
not intervene
• direct control of investigator
• Intervention in experimental group
• Compare outcome with control group
Experimental studies

5. Descriptive studies
• Observing the distribution of
disease in a population
• Identifying the characteristics
associated with the disease
• Generate hypothesis
Case reports
Case series
Cross sectional studies
Longitudinal studies
Ecologic studies
describe

6. Case reports
Detailed presentation of a single case
• New or unfamiliar diseases
• Rare manifestations

7. Case series
• Study of larger group of patients
(> 10) with a particular disease
• Common way of delineating the
clinical pictures of a disease
• Absence of a comparison group

8. Cross sectional studies (Prevalence studies)
• Observation of a snapshot of a population at a single point in time
• Unit of observation and analysis: The individual
• Exposure and disease outcome are determined at same time
• Observation for the presence of:
o One or more outcomes
o One or more exposures
• Do not know disease duration; temporal sequence of exposure – disease

9. Longitudinal studies
• Observation of the same population at several points of time
• Unit of observation and analysis: The individual
• Change over time can be tracked
• Observation of
• Relation between exposure and outcome
• Outcome of exposure over different lengths of time

10. Ecologic studies (Correlational studies)
• Unit of analysis : group (population)
• Relate whether populations with
high rates of disease also have high
rates of exposure
• Ecologic fallacy : relations at
group level is not possessed by
individuals of the group

11. Analytical studies
• Test hypothesis
• Measures the pattern of exposure
and disease
• Inference by comparing groups
Cross sectional
studies
Case control studies
Cohort studies
compare

12. Analytical Cross sectional studies
• Prevalence distribution of exposure and outcome
• Comparison of outcome differences in exposed and unexposed

13. Case control studies (Retrospective studies)
• Starts by picking cases and controls
• Exposure and outcome occurred
before start of study
• Backward looking study
(effect  cause)

14. Cohort studies
• Cohorts are identified before
outcome occurs
• Study groups observed over a time
period
• Forward looking study
(causeeffect)

15. Randomized controlled trials
• Randomly assigns participants into
experimental and control group
• Intervention in experimental group
• The groups are followed up to
measure the outcome of intervention
• Blinding
Reference
population
Experimental
group
Control
group

16. Summary
Observational studies Experimental studies
Descriptive studies
• Case reports
• Case series
• Cross-sectional studies
• Longitudinal studies
• Ecologic studies
Randomized controlled trial
Field trial
Community trial
Analytical studies
• Cross-sectional studies
• Case control studies
• Cohort studies

17. THANK YOU