In significance testing,
the probability value (sometimes called the p value) is the probability of
obtaining a statistic as different or more different from the parameter
specified in the null
hypothesis as the statistic obtained in the experiment. The probability
value is computed assuming the null hypothesis is true. The lower the probability
value, the stronger the evidence that the null hypothesis is false. Traditionally,
the null hypothesis is rejected if the probability value is below 0.05.
Probability values can be either one tailed or two tailed.