The p-value or probability value is a measure of statistical significance. If the null hypothesis is assumed to be true, the p-value indicates the probability of observing a particular outcome or result. The lower the p-value, the lower the probability of a result occurring by chance and therefore, greater the significance. A p-value of 0.05 indicates that there is a 5% probability of a chance outcome. For historical reasons, a p-value of 0.05 has been used as a cutoff for significance. Values less than 0.05 are considered significant. If the p value is 0.001 or less (less than a 0.1% probability that the results occurred by chance), the result is seen as highly significant.