Clinical Evidence Hierarchy

Expert opinion sits near the bottom of the evidence pyramid regardless of the expert's credentials. The Lancet and NEJM retractions were caused by use of a third-party data aggregator whose data could not be independently verified. In vitro findings generate hypotheses but do not constitute treatment recommendations. Observational studies cannot distinguish between confounded associations and true causal relationships. Randomized controlled trials resolve confounding by randomly assigning subjects to intervention or control groups. Each rung of the evidence pyramid tests hypotheses generated by the rung below it.