Evidence-appraisal glossary
Study protocol
A study protocol is the written plan that specifies a trial's objectives, design, eligibility criteria, outcomes, and analysis before the data are collected.
Also called: trial protocol, research protocol.
The protocol is the reference document against which the final report should be judged: it fixes the primary outcome, the sample size, and the planned analyses in advance so that results cannot be quietly reshaped to look better. Comparing a published paper to its protocol (or its pre-registered summary) can reveal outcome switching, where a secondary result is promoted to headline finding. A protocol existing does not guarantee it was followed, which is why some are published or registered openly.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.