Understanding evidence hierarchies: from case report to systematic review
This page is demonstration content.
The ladder and its limits
Evidence hierarchies rank study designs by their resistance to bias: systematic reviews and randomised trials sit above cohort and case-control studies, which sit above case reports and expert opinion. The ranking describes design, not truth. A flawless cohort study can say more than a flawed trial.
What examiners look for
- Name the design correctly and state its main bias.
- Say what question the design can answer and what it cannot.
- Know when the hierarchy misleads, for example in rare conditions where only case series exist.
The practical skill is matching the question to the best available design, not reciting the ladder.