1. Cross-sectional studies
Representative sample
Select random
sample of population
Study population
Identify exposure status
and disease status
within sample.
Disease
No disease
Exposed
Not exposed
One point in time – non-directional (possibly backward).
Easy and economical.
Relatively quick.
Can’t say much at all about causality.
Great as first, quick look.

2. Cross-sectional studies
Cross-sectional studies investigate
disease risk at a single point in time.
future
   
present
past
With disease (case)No disease

3. disease-free controls
Case-control studies
Cases
Deliberately recruit
more cases than in
a random sample
Study population
Controls
Select similar
disease-free controls
Exposed
Not
exposed
Compare exposure status among cases & controls

4.    Recruiting many disease cases increases the
Case-control studies
Recruiting many disease cases increases the
study’s ability to identify risk factors.
future
  
present
Some case-control
studies examine past
exposures and are
also known as
retrospective studies.
Exposure
past

5. Cohort (longitudinal) studies
Recruit random
sample of people
without the disease
People without the disease
Study population
Record exposure
& disease over time
Time 1
Disease
No disease
Exposed
Not exposed
Population
Time 2
Etc.

6. Cohort (longitudinal) studies
   
future
Follow-up
   
   
Recruit-
ment
present
Cohort studies select individuals and observe how
their exposure and disease status changes over time.
They are sometimes known as prospective studies.
past