Trial Design
Endpoint (Clinical Trial)
A clinical trial endpoint is a defined, measurable outcome that determines whether the intervention being studied has the intended effect; it is the variable on which the trial's success or failure is statistically evaluated.
Endpoints are categorized as primary (the trial's principal scientific question), secondary (supporting hypotheses), exploratory (hypothesis-generating), and safety. Primary endpoints determine trial powering and are pre-specified in the protocol and SAP.
Endpoint selection drives feasibility: a hard endpoint (e.g., overall survival) provides regulatory certainty but requires long follow-up and large sample sizes; a surrogate endpoint (e.g., PFS, biomarker response) accelerates timelines but may face additional regulatory scrutiny under accelerated-approval pathways.
Modern protocols increasingly adopt the ICH E9(R1) estimand framework, which couples each endpoint with explicit specification of how intercurrent events (treatment discontinuation, switching, death) are handled in the analysis.
Related terms
Clinical Trial Protocol
A clinical trial protocol is the master document that defines a clinical study's objectives, design, methodology, statistical considerations, and operational conduct, and that all investigators must follow to ensure scientific validity and participant safety.
Statistical Analysis Plan (SAP)
A Statistical Analysis Plan (SAP) is a detailed technical document that specifies, before database lock, every statistical analysis to be performed on a clinical trial's data, including primary and secondary endpoint analyses, handling of missing data, multiplicity adjustments, and sensitivity analyses.
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