FAQ/power/unpaired282013-03-08 10:17:39localhostconverted to 1.6 markup272007-12-03 17:19:30PeterWatson262007-12-03 17:19:04PeterWatson252007-08-09 13:17:29PeterWatson242007-08-09 13:16:35PeterWatson232007-08-09 13:14:33PeterWatson222007-08-09 13:13:23PeterWatson212007-03-20 16:24:47PeterWatson202007-03-20 16:02:06PeterWatson192007-03-20 16:01:43PeterWatson182007-01-15 09:46:36PeterWatson172007-01-15 09:46:10PeterWatson162007-01-09 15:56:51PeterWatson152007-01-09 15:56:32PeterWatson142007-01-09 15:55:00PeterWatson132007-01-09 15:54:35PeterWatson122006-12-08 10:15:57PeterWatson112006-12-08 10:15:19PeterWatson102006-12-07 15:43:43PeterWatson92006-12-07 15:43:17PeterWatson82006-12-07 15:40:16PeterWatson72006-09-14 15:39:32PeterWatson62006-08-30 12:44:11PeterWatson52006-08-30 12:15:05PeterWatson42006-08-30 12:13:26PeterWatson32006-08-25 14:27:23PeterWatson22006-08-25 09:00:32PeterWatson12006-08-24 15:34:23PeterWatson[ADJUST THE EXAMPLE INPUT AS DESIRED; THEN COPY AND PASTE INTO A SPSS SYNTAX WINDOW AND RUN; OUTPUT BOTH TO SPREADSHEET AND OUTPUT WINDOW]. This program uses Cohen's d or Hedge's g as the effect size, depending on calculation of pooled group standard deviation, for example in an equal groups unpaired t-test . Alpha is the (two-tailed) type I error, mdiff is the difference in group means, sd is the average group standard deviation with power inputted in the power column. The program then outputs the common group sample size. Calculations can also be done using a spreadsheet. You can specify input in terms of Cohen's d. This may be done in R.