Standard Article

P Value

  1. Steven N. Goodman

Published Online: 15 JUL 2005

DOI: 10.1002/0470011815.b2a15110

Encyclopedia of Biostatistics

Encyclopedia of Biostatistics

How to Cite

Goodman, S. N. 2005. P Value. Encyclopedia of Biostatistics. 6.

Author Information

  1. Johns Hopkins School of Medicine, Baltimore, MD, USA

Publication History

  1. Published Online: 15 JUL 2005


The P value is the probability, under a given simple hypothesis, of the observed or a more extreme value of a test statistic. Problems discussed include that of the choice of test statistic, the relevance of alternative hypotheses, ambiguity about the sample space, and the interpretation generally. The distinction between one-sided and two-sided tests is a source of confusion. Bayesian considerations are discussed.


  • inference;
  • significance test;
  • tail area;
  • null hypothesis;
  • alternative;
  • sample space;
  • one-sided;
  • two-sided;
  • Bayes factor