Clinical Research Glossary

p-value (probability value) p-value (probability value)


A number that researchers use to show that a result did not occur by chance.

Example of p-value (probability value) in a sentence

The p-value is used in research to show whether a difference in effect between treatments is due to chance.

More Info

The p-value is part of the scientific process. It is a number used when analyzing research data and reporting research results.

The p-value shows whether the results could have occurred by chance.

When a p-value is very small, it means that it is less likely to have occurred by chance.

For example, if a study has a p-value of 0.05, this means that if you did the study 100 times, the results would likely be the same 95 times.

It is important to note that even if something has a small p-value and is statistically significant, the result may not make a big difference to patients. For example, a drug may shrink a tumor but not extend a person’s life.

Other info to think about when joining a study

You might see the term “p value” in a publication about research where the study results and statistics are reported.

The article may include a results section that has more information about what the p-value for the study is and what that means for the results.

The p-value could also come up in Plain Language Summaries of a study’s results

If you have any questions about how the p-value is being reported, feel free to talk to the study team.

An icon consisting of a circle with a calculator, graph paper with a bar chart and a bell curve drawn on, and a pencil. This icon represents all the math terms in this glossary.
This graphic represents math and statistics terms in this glossary.

Was this entry helpful?

Thanks for your feedback!