Detection probability is the probability, if diversion of a given amount of nuclear material has occurred, that IAEA safeguards activities will lead to detection. The detection probability is usually denoted as 1 - β, with β being the non-detection probability. The detection probability for safeguards activities involving nuclear material accountancy can be quantified, and the accountancy detection probability 1 - βa is preselected as an input parameter for establishing sampling plans. The values of 1 - βa currently in use are 90% for 'high' and 20% for 'low' probability levels.