A single predictor in a multiple binary logistic regression
A power calculator is given [http://www.dartmouth.edu/~eugened/power-samplesize.php here] for upto two binary covariates using Demidenko (2007, 2008) and [http://biostat.hitchcock.org/MeasurementError/Analytics/SampleSizeCalculationsforLogisticRegression.asp here.]
Hsieh FY (1989) gives formulae to compute total sample size for given power in a multiple binary logistic regression for odds ratios up to 3 in magnitude. These calculations can be done using a [attachment:llog1.xls spreadsheet.]
References
Demidenko E. (2007). Sample size determination for logistic regression revisited. Statistics in Medicine 26 3385-3397.
Demidenko E. (2008) Sample size and optimal design for logistic regression with binary interaction. Statistics in Medicine, 27 36-46.
Hsieh FY (1989) Sample size tables for logistic regression. Statistics in Medicine 8 795-802.