An endpoint is a pre-specified outcome measured in a trial to answer its research question. The primary endpoint answers the main question and drives the sample size; secondary and exploratory endpoints add supporting evidence and hypotheses.
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Endpoint
noun · clinical research
A pre-specified variable, measured at a defined time, used to assess whether a treatment has an effect.
Related terms
In short
Types
| Type | Role | Example |
|---|---|---|
| Primary | Answers the main question; powers the trial | Change from baseline in HbA1c at week 26 |
| Key secondary | Supports claims; tested with multiplicity control | Proportion reaching HbA1c below 7% |
| Secondary | Additional supporting evidence | Change in body weight |
| Exploratory | Hypothesis generating | Change in an inflammatory biomarker |
| Surrogate | Stands in for a clinical outcome | LDL cholesterol for cardiovascular events |
| Composite | Combines events into one endpoint | Cardiovascular death, heart attack or stroke |
| Patient-reported | Measures how participants feel or function | Change in PHQ-9 total score |
Explained
A well-written endpoint names the measurement, the time point and the summary: "change from baseline in PHQ-9 total score at week 12" can be built directly into a study. The eCRF needs the nine item scores at baseline and week 12, collected within visit windows, and the analysis derives the total and the change. An endpoint written as "improvement in mood" cannot be built until someone makes those decisions.
That is why endpoints should be settled before the database is built, and why the protocol template pairs each objective with an endpoint. Endpoints based on validated instruments also need licences and correct scoring; the instrument templates cover common ones, and MCID explains how meaningful change is judged.
The main outcome that answers a trial's primary question. The sample size is calculated to detect an effect on it.
Yes, but multiple primary endpoints require a strategy for controlling the overall error rate and a clear rule for what counts as success.
A marker, such as a lab value, that is expected to predict a clinical benefit and is used in place of the clinical outcome.
A precise description of the treatment effect to be estimated, including how events such as treatment discontinuation are handled (ICH E9(R1)).
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