Sample Size for Cohort, Case-Control and Clustered Studies

Real studies get more complicated than two clean groups. This level sizes cohort and case-control studies through their exposure and outcome proportions, and reveals why clustered designs need more participants than their headcount suggests.

Who this level is for

Researchers and clinicians designing cohort, case-control or cluster studies, plus data and program staff supporting them. Recommended after Levels 1-3.

What you'll learn

• How cohort sample size links to risk difference and relative risk
• A hands-on cohort demo using riskcalc
• How case-control sizing thinks in exposure proportions and the odds ratio
• A hands-on case-control demo
• Why clustered data shrinks your effective sample size (design effect and the intracluster correlation), as intuition rather than formulas
• Where cluster options live in the online calculators and what extra inputs they need

You finish with: Sample size for a cohort or case-control version of your study, plus a note on clustering.