On approximate sample sizes for comparing two independent proportions with the use of Yates' correction.

An investigator wishes to compare two independent proportions, based on perhaps unequal sample sizes, by means of the chi squared test with the Yates' correction. A simple approximation is given to the sample size(s) required for the Yates-corrected chi squared test to have specified power; it is then compared with other approximations and with the exact sample size for the equal sample case. In that case the proposed approximation is quite similar to the approximate formula recently put forward by Casagrande, Pike and Smith (1978, Biometrics 34, 483-486).