Table PTT1. Two group continuity corrected Chi-square test of equal proportions (equal n’s)

Computed using the large sample normal approximation shown in the nQuery Advisor® manual appendix. See Fleiss JL, Tytun A, Ury SHK (1980) A simple approximation for calculating sample sizes for comparing independent proportions. Biometrics. 36:343-346. Figure PTT1 shows computations for two examples, second example is from Fleiss JL (1981) Statistical Methods for Rates and Proportions, 2nd edition, John Wiley & Sons, Inc. New York. Solutions for range of parameter values tested in PTT0 checked against answers from PTT0 modified using correction factors in Table 3.2 from Machin D, Campbell MJ (1987) Statistical Tables for the Design of Clinical Trials, Blackwell Scientific Publications Oxford.

Figure PTT1. In the first and third columns, nQuery Advisor® 7.0 has solved for sample size and in the second and third columns, nQuery Advisor® 7.0 has solved for power.