p-values

Without a doubt, p-values are one of the most used and misunderstood concept in medical and biological research. So, what is a p-value and how is it defined?


The p-value is the probability of observing a result as extreme as, or more extreme than, the one obtained in your data, assuming the null hypothesis is true.



A p-value is a statistic whose numerical value can be used to indicate how incompatible the observed data is to the Null hypothesis, that corresponds to a specified statistical model.

In very simple cases, the p-value can be defined as the probability (under the Null hypothesis) of observing a value the same or a more extreme value than what was actually observed. However, there are differing definitions that can be given, and depending on the context one or the other is used.