Evidence-appraisal glossary
Alpha level
The alpha level is the threshold, chosen before analysis, at which a result is called statistically significant; it is the type I error rate the study is willing to accept, commonly 0.05.
Also called: significance level, alpha.
A p-value is compared against alpha to decide significance, so setting alpha at 0.05 means accepting a 5 percent chance of a false positive under the null hypothesis. Two cautions: alpha must be fixed in advance rather than chosen to fit the data, and it is not the probability that the null hypothesis is true. When many tests are run, the shared alpha is often tightened to control the overall false positive rate.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.