Assessment of small health risks based on exact sample sizes

Exact sample sizes and critical numbers of cases for the rejection of a known event probability (10(-2) to 10(-6)) in favour of an increased probability (1.5- to 50-fold) at levels {alpha;beta} = {0.05; 0.10} and {alpha;beta} = {0.10; 0.05} are presented. The numbers are thoroughly validated using the characteristics of the confidence interval for the unknown true event probability. Equivalence is shown to be obtainable for the tolerated maximal value of the relative risk and the upper limit of the confidence interval for the true event probability. Also demonstrated is the use of the tables for planned actions to reduce given empirical risks. In addition, use of the tables is shown for judging results from given data sets.