A version of this tool is included in the R package epiR . So please cite this page as follows:

Stevenson M, Nunes T, Heuer C, Marshall J, Sanchez J, Thornton R, Reiczigel J, Robison-Cox J, Sebastiani P, Solymos P, Yoshida K, Firestone S. (2015) epiR: An R package for the analysis of epidemiological data. R package version 0.9-69.

Dupont WD (1988). Power calculations for matched case-control studies. Biometrics, 1157-1168.