The [[attachment:prop1s.xls|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 [[FAQ/onesamppow|using R.]]

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

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

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