statistical error type II error Harold Lehmann, Ken Wilkins, Joanne Dehnbostel, Airton Stein, Homa Keshavarz Philippe Rocca-Serra 'Incorrectly failing to reject the null hypothesis' means not rejecting the null hypothesis when it is actually false. In statistical hypothesis testing, the event of failing to reject the null hypothesis is usually not directly verifiable because it is not generally observable whether the null hypothesis is actually true. The probability of a type II error is designated as beta. false negative error the event of incorrectly failing to reject the null hypothesis. type 2 error