This document describes different types of epidemiological study designs, including observational studies like cross-sectional, case-control, cohort, and experimental studies like randomized controlled trials. It provides details on descriptive versus analytical epidemiology and cross-sectional studies specifically. Cross-sectional studies measure prevalence at a single point in time by surveying exposures and disease status simultaneously in a population cross-section. They are useful for assessing disease burden, comparing prevalence between populations, and examining trends over time.

1. STUDY DESIGNS

2. Types of epidemiological studies
• Types of studies Alternative name Unit of study
• OBSERVATIONAL STUDIES
– Descriptive studies
– Analytical studies
• Ecological Correlation Populations
• Cross-sectional Prevalence Individuals
• Case-control Case-reference Individuals
• Cohort Follow-up Individuals
• EXPERIMENTAL STUDIES (Intervention Studies)
– Randomized control trials Clinical Trials Patients
– Field trials Healthy People
– Community trial Community studies Communities

3. Difference between Descriptive and Analytical Epidemiology
Descriptive Epidemiology Analytical Epidemiology
Only one group studies At least two groups are studied for
comparison
At the start of study there is no
explicit hypothesis regarding cause
effect relationship
At the start of the study there is definite
hypothesis regarding an exposure
possibly causing an outcome.
The study ends in development of
possible hypothesis regarding cause
and effect relationship but does not
confirm or reject such hypothesis
At the end of the study it confirms or
rejects the hypothesis with which it
started

4. Cross-sectional studies
An “observational” design that surveys
exposures and disease status at a single point
in time (a cross-section of the population)
Time
Study only exists at this point in time

5. Reasons for doing a cross-sectional study
• To assess the burden of disease in a
population and to assess the need for
health services.
• To compare the prevalence of disease in
different populations.
• To examine trends in disease prevalence
or severity over time.

6. Cross-sectional Studies: characteristics
• Exposure and disease outcomes are determined
simultaneously
• Provides a snap shot view and hence measures
prevalence, not incidence of disease; Example:
community surveys
• Know the existence of disease but not the duration
• Often used to study conditions that are relatively
frequent with long duration of expression (nonfatal,
chronic conditions)
• Not suitable for studying rare or highly fatal diseases or
a disease with short duration of expression
• Examining effects on physiologic variables (e.g. Liver
enzyme levels, blood pressure, lung function)

7. Where can we do a cross sectional study
• Any setting or location
– Community
– Schools
– Worksite
– Hospitals