Evidence-appraisal glossary
Prior probability
In Bayesian analysis, the prior probability is the probability assigned to a hypothesis or parameter before the current study's data are taken into account.
A prior can draw on earlier studies, biological knowledge, or a deliberately neutral stance that lets the data dominate. Because the prior feeds into the final result, it matters most when the new data are limited; transparent analyses state the prior explicitly and test whether the conclusions hold under other defensible choices.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.