Jeanne M. Clark, MD, MPH Division of General Internal Medicine Cohort Study Overview Jeanne M. Clark, MD, MPH Division of General Internal Medicine

Design of Cohort Studies Examples: JHU Precursors Study Framingham Study Identify: Exposed Develops Disease No Disease Not Exposed Defined Population Non-random selection Can start here: (less common)

Prospective (Concurrent) Cohort 2000 2001 2008 Exposed Develops Disease No Disease Not Exposed Defined Population Non-random selection Typically active, scheduled follow-up of some kind

Retrospective (Non-Concurrent) Cohort 1988 1998 2008 Exposed Develops Disease No Disease Not Exposed Defined Population Non-random selection Generally passive or post-hoc follow-up of some kind

Analysis of Cohort Studies Then follow to see: Start with: Develops Disease No Disease Totals Incidence Rates Exposed a b a+b a/a+b Not Exposed c d c+d c/c+d

Comparison of 4 Major Study Designs Goal or Feature RCT CS CC X-S Estimate Prevalence F F F A+ Estimate Incidence B- A+ F F Prove Causality A+ B+ B- D Generalizability B- A- A- A Feasibility C B A A RCT=Randomized, controlled trial; CS=Cohort study; CC=Case-control study; X-S=Cross-sectional study