A p value is the probability of observing results at least as extreme as those reported in a study, assuming that the null hypothesis is true (usually ‘no difference’). In a hypothesis test this value is compared with the prespecified threshold for significance (a) in order to conclude whether there is evidence to reject the null hypothesis. Calculators are available to provide p values associated with study results expressed as Z scores (normal distribution), t-scores, chi squared and many other distributions. A common misapprehension is that the p-value supports reasoning about the probabilities of alternative hypotheses, whereas its use is primarily to decide whether or not to reject the null hypothesis.

How to cite: P Value [online]. (2016). York; York Health Economics Consortium; 2016. https://yhec.co.uk/glossary/p-value/