Study Designs
Five ways researchers structure a study
Each design answers a different kind of question. Here is what sets them apart.
- 01
Randomized Controlled Trials
Volunteers are assigned to groups by chance, so the groups start out alike and differences at the end are easier to interpret.
- Random assignment to groups
- A comparison or control group
- Often paired with blinding
- 02
Observational Studies
Researchers watch what happens naturally without assigning anyone to a group, then look for patterns in the data.
- No assigned intervention
- Useful when an experiment is not practical
- Patterns, not proof of cause
- 03
Cross-Sectional Studies
A snapshot taken at one moment in time, describing how common something is across a group of people.
- Single point in time
- Good for measuring how common something is
- Cannot show what came first
- 04
Cohort Studies
A group of people is followed forward over months or years to see how different exposures relate to later outcomes.
- Follows people over time
- Can be forward looking or use past records
- Shows sequence of events
- 05
Case-Control Studies
Researchers start with people who have an outcome and compare their history with a similar group who do not.
- Works backward from an outcome
- Efficient for rare outcomes
- Relies on careful matching