On the sample size for studies based upon McNemar's test.

When computing the sample size for studies using McNemar's test, one needs to know the probability of discordance and the odds ratio to be detected. In many studies, the investigator is unable to specify the probability of discordance, but can state, at least approximately, the marginal probabilities of each variable. This information leads to restrictions on the possible values of the cell probabilities and provides a range of admissible values for the off-diagonal cells. We compute the sample size needed in these circumstances and compare them to the results cited by Schlesselman and Connett et al. These sample sizes for the method are quite close to those found in the Monte Carlo study of Connett et al.