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Clinical trials and systematic reviews for clinicians
Audience: doctors-clinicians, students-learners ยท Review state: published
The two evidence engines
A clinical trial tests an intervention in people under controlled conditions; a systematic review collects every relevant study on a question under a pre-registered protocol and appraises them together. Trials generate evidence; systematic reviews assemble it.
Between them sits the quality question: a well-run small trial can outrank a sloppy large one, and a review is only as good as the studies and methods inside it.
Reading a trial
Start with the design: randomized allocation and blinding protect against the strongest biases. Then the population: trial participants are selected, and whether your patient resembles them decides how far results travel.
Read absolute effects before relative ones, check the confidence intervals, and note the follow-up length. A trial registered before it ran, with outcomes reported as registered, is more trustworthy than one with shifting endpoints.
Reading a systematic review
Check for a published protocol, a real search across multiple databases, and explicit inclusion criteria. A meta-analysis pools results statistically; wide variation between studies, called heterogeneity, warns that the pooled number may not describe any single setting well.
Publication bias, where positive studies are more likely to appear than negative ones, inflates apparent effects. Good reviews hunt for it and say what they found.
Placing evidence in practice
Evidence informs decisions; it does not make them. Applicability, patient values, feasibility and the quality of the underlying studies all enter. Educational overviews like this one build reading skill only.
When trial evidence and a patient's situation pull in different directions, the conflict is information: document the reasoning, discuss it honestly, and revisit as evidence evolves.
Limitations
Educational method only. Not a recommendation for or against any treatment, trial participation or review conclusion.