Separate a Primary Endpoint From an Exploratory Finding

The research question

A primary endpoint anchors the main study question and sample size planning. Secondary endpoints expand understanding, while exploratory analyses help generate future questions. Knowing this hierarchy helps readers assess the strength of a claim. Search the protocol, registry, and statistical analysis plan for the original outcome definitions and testing strategy.

How to interpret the evidence

Multiple analyses create many opportunities to observe an apparently compelling pattern. Prespecified methods may control the statistical consequences of testing several outcomes. Readers should examine whether each reported conclusion met the planned requirements. An exploratory result can remain scientifically interesting while the article clearly communicates its role in the research sequence.

SPIRIT 2025 addresses transparent reporting of randomized trial protocols. It is useful when examining how investigators planned outcomes and analysis before results were available.

Endpoint changes can have legitimate scientific or operational explanations. The important task is to understand their timing, justification, and potential effect on inference. A revision made before access to outcome data requires a different appraisal from a revision guided by results. Readers should examine the documentation carefully and communicate what is actually available.

Practice the appraisal

Original protocol exercise: open a trial registry entry, its protocol, and the publication. Find the primary endpoint and its assessment time in each document. Note whether the documents were dated before enrollment, before analysis, or after the results. Choose a secondary claim in the abstract and locate its place in the testing hierarchy. Ask whether the reported inference followed the planned procedure. Write a concise explanation of any available change and its rationale. The exercise builds a transparent record of how the research question developed.

Apply the lesson

An educational slide should make the outcome hierarchy visible in the wording of the claim. Describe the planned primary question directly. Label exploratory observations as questions for further work. When an analysis plan changed, report the available explanation and timing. This approach helps an audience understand which result anchors the study and how supporting observations fit within the larger scientific picture.