The probability of rejecting the null hypothesis when the null hypothesis is really true, i.e., of incorrectly deciding that at least 100P% of the population is less than the action level. For example, if the VSP user specifies P = 0.90 and confidence = 95% (alpha = 0.05), then the user can tolerate a probability of 0.05 (5%) of rejecting the null hypothesis that the site is dirty when in fact less than 90% of the population is less than the action level.