[Evaluation of non-occurrence by TI-59 programmable calculator]

A TI-59 programmable calculator program is presented for calculating either risk probability, sample size or confidence level (given 2 of the 3 variables) in cases in which an event of concern did not occur, or as expressed mathematically, had zero numerators. Its main usefulness is as a tool for interpreting previously published data containing no adverse event of concern while contemplating medical alternatives. These conditions are not infrequent in rare medical events--either diseases or complications. However, applicability of the program extends beyond these confines, exemplified in experimental planning for considering expected sample size or in calculating certainty in terms of confidence level.