How to Read a Randomized Controlled Trial Step by Step

Randomization aims to create comparable groups by chance, while allocation concealment prevents recruiters from predicting the next assignment. Blinding can reduce performance or outcome-assessment bias, but feasibility varies by intervention. Check baseline characteristics without treating every small imbalance as proof of failed randomization, and look for imbalances large enough to affect interpretation in a modest sample.

The participant-flow diagram should connect enrollment, allocation, follow-up, exclusions, and analysis. Attrition can bias results when its amount or reasons differ by group. Intention-to-treat analyses generally preserve randomized assignment, while per-protocol analyses answer a different question about adherence to the protocol. Compare both when reported and inspect how missing outcomes were handled rather than relying on the label alone.

Read group-level results, effect sizes, confidence intervals, adverse-event reporting, and sensitivity analyses. Check multiplicity, early stopping, funding, protocol changes, and whether conclusions match the primary outcome. A well-reported positive RCT is one piece of an evidence base; replication, duration, population relevance, and comparison with other studies still matter. Trial results do not provide individualized advice through this page.

Finally, distinguish explanatory efficacy questions from pragmatic effectiveness questions. Highly controlled eligibility and follow-up may clarify whether an intervention can produce an effect under trial conditions, while a broader design may better reflect routine settings. Neither design automatically answers how a result applies outside the population and conditions actually studied.