What Is Per-Protocol Analysis?

By Kristi Waterworth – Updated Nov 14, 2025 at 1:44 AM EST

Key Points

Per-protocol analysis excludes noncompliant clinical trial participants' data.
Mixing per-protocol with other analyses gives a clearer intervention picture.
Regulators typically reject sole per-protocol analysis for product approvals.

Investors interested in the biotech industry really need a lot of specific information to make up their minds about a company. One thing they need is a way to examine clinical trial data: enter per-protocol analysis.

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Reducing the sample size

The sample size is everything when it comes to medical trials. The more people involved, the more impactful the results achieved and the conclusions reached. When people start going missing, it reduces the study's impact and can render it meaningless if enough people are removed.

Defeating the purpose of the study

Studies are generally done to better understand who benefits from medications and interventions and how. If people drop out because the medication isn't helping or is making things worse, they must be counted, too. It's hard to see the true percentage of people a medication is helping if you don't count the people who withdrew due to noncompliance (which also happens in real-life medical practice).

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About the Author

Kristi Waterworth has been a contributing real estate and financial expert at The Motley Fool, covering real estate, investing, and personal finance topics, since 2020. Kristi has been interviewed by various TV media outlets and podcasts for her real estate investing expertise – from residential real estate to digital real estate and everything in between. Kristi’s journalist career spans over 25 years, and she has written about real estate investing, homeownership, and home construction specifically for the last decade. She was also previously a licensed Realtor and general building contractor before the Great Recession and housing market collapse. She holds a bachelor’s degree in American history from Columbia College in Missouri.

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