Prospective Study
A prospective study is an observational study that identifies a cohort now and follows them forward in time, recording exposures and outcomes as they happen.
Why not just run an RCT?
When randomization is impossible (ethics, cost), observing real-time exposures forward avoids the recall problems of looking backward.
Unlike a RCT, the researcher does not assign treatments. Unlike a Retrospective Study, data is collected as events unfold.
Strengths
- Clean temporal order: exposure observed before outcome, ruling out reverse causation
- High data quality: measurements taken in real time
- Can study many outcomes from a single exposure
Weaknesses
- Slow and expensive (decades for outcomes like cancer)
- Loss to follow-up: subjects drop out, retire, die of unrelated causes
- Still observational: confounders remain; statistical adjustment is no replacement for randomization
Framingham Heart Study
Since 1948, thousands of Framingham, MA residents have been followed prospectively. Most of what we know about heart disease risk factors comes from this design.