What is a p value in statistics?

A common misperception is that p = .05 means there is a 5% probability of obtaining the observed result by chance. The correct interpretation is that there is a 5% probability of getting a result this large (or larger) if the effect size equals zero.

What is a p value?

A p value is the answer to the question: if the null hypothesis were true, how likely is this result? A low p says “highly unlikely”, making the null improbable and therefore rejectable.

In substantive terms, a p value really tells us very little. As the p value is a confounded index, it is never a good idea to interpret results on the basis of p values.