EFFICIENT POWER COMPUTATION FOR EXACT AND MID-P TESTS FOR THE COMMON ODDS RATIO IN SEVERAL 2X2 TABLES

When designing a study that may generate a set of sparse 2 x 2 tables, or when confronted with 'negative' results upon exact analysis of suc h tables, we need to compute the power of exact tests. In this paper w e provide an efficient approach for computing exact unconditional powe r for four exact tests on the common odds ratio in a series of 2 x 2 t ables. These tests are the traditional exact test; a test based on a p robability ordering of the sample space; and two tests based on orderi ng the sample space according to distance from the mean, or median. Fo r each test, we consider both a conservative version and a mid-P adjus ted version. We explore three computational options for power determin ation: exact power computation, calculation of exact upper and lower b ounds for power, and Monte Carlo confidence bounds for power. We prese nt an interactive program implementing these options. For study design , the program may be run several times to arrive at a sample configura tion with adequate power.