The spreadsheet gives the power for inputted group proportions (which should sum to 1), Type I error and a given total sample size. The expected proportions assume equal group sizes. Power may also be obtained using R.

The expected effect size, ${\displaystyle \omega }$, defined below is from Cohen (1977,1988, Chap 7).

${\displaystyle \omega =\sqrt{\sum _{\text{1}}}}$^{text{no. groups} \frac{\mbox{(observed proportion - expected proportion)}}text{2}}{ \mbox{ expected proportion}}}${\displaystyle }$

The thresholds 0.1, 0.3, 0.5 correspond to small, medium and large ${\displaystyle \omega }$ effect sizes.