Per-Protocol Analysis
A statistical approach that only includes participants who completed the trial exactly as designed, without major protocol deviations.
In Detail
Per-protocol (PP) analysis is a statistical methodology that includes only those participants who completed the clinical trial in compliance with the protocol, meaning they received the full course of treatment, attended all required visits, met all eligibility criteria, and did not have major protocol deviations. Participants who dropped out, missed doses, switched treatments, or violated key protocol requirements are excluded from the per-protocol analysis. This approach provides an estimate of the treatment's effect under ideal conditions, what happens when patients actually take the drug as directed. Per-protocol analysis typically shows larger treatment effects than intention-to-treat analysis because it excludes "noise" from non-compliant participants. However, this exclusion can introduce bias because the reasons participants drop out or deviate from the protocol may be related to the treatment itself. For example, if participants drop out because of side effects, excluding them would make the treatment appear safer and more effective than it actually is in the broader population. For this reason, regulatory agencies consider ITT analysis the primary analysis and treat per-protocol analysis as supportive or sensitivity analysis. The two analyses are expected to be concordant, if the ITT analysis shows the treatment works and the per-protocol analysis confirms it, the evidence is considered robust. If the results diverge, it raises questions about the reliability of the findings. Per-protocol analysis is particularly useful for non-inferiority trials, where it provides a more conservative estimate (the opposite of its role in superiority trials). Understanding both ITT and PP analysis helps patients and physicians evaluate the strength of clinical trial evidence.
Frequently Asked Questions
What does "Per-Protocol Analysis" mean in clinical trials?
A statistical approach that only includes participants who completed the trial exactly as designed, without major protocol deviations.
Why is "per-protocol analysis" important for patients?
Understanding per-protocol analysis helps patients and caregivers navigate clinical trial participation with confidence. It is part of the broader clinical research process that ensures treatments are safe and effective before reaching patients.
Related Terms
Intention-to-Treat (ITT) Analysis
A statistical approach that includes all participants in the analysis based on their original group assignment, regardless of whether they completed the treatment.
Statistical Significance
A mathematical determination that the observed results of a clinical trial are unlikely to have occurred by chance, typically defined as a p-value less than 0.05.
Clinical Trial
A research study that tests a medical treatment, drug, device, or intervention in human volunteers to determine whether it is safe and effective.
this entity is one of the U.S. clinical trials and research registries concepts that recurs across this site. The definition above is the technical answer; the paragraphs below add the practical context for how the concept connects to the the NIH ClinicalTrials.gov registry data behind every per-entity page on the site.
In the the NIH ClinicalTrials.gov registry data, this concept shapes one or more of the fields that drive the per-entity grades and rankings on this site. The methodology page describes which fields feed into which output; this glossary entry documents the underlying term.
Source: ClinicalTrials.gov, 2026.