Exact equivalence test for risk ratio and its sample size determination under inverse sampling

When data are dichotomous, this paper notes the utility of inverse sampling in establishing equivalence with respect to the risk ratio. This paper develops an exact equivalence test that accounts for the risk ratio under inverse sampling and further discusses the relationship between the exact equivalence test and the exact conditional confidence limits. Also included are an exact and two asymptotic procedures for calculation of the minimum required number of index subjects for a desired power 1−β at a given α‐level. Finally, this paper provides a table that summarizes the minimum required number of index subjects for powers equal to 0⋅90 and 0⋅80 in application of the proposed exact equivalence test at 0⋅05‐level in a variety of situations. © 1997 by John Wiley & Sons, Ltd.