FAQ/power/pairt252013-03-08 10:17:36localhostconverted to 1.6 markup242008-01-21 16:51:03PeterWatson232007-12-03 17:02:10PeterWatson222007-12-03 17:00:57PeterWatson212007-12-03 16:55:46PeterWatson202007-12-03 16:53:22PeterWatson192007-12-03 16:50:09PeterWatson182007-12-03 16:46:52PeterWatson172007-03-20 16:25:14PeterWatson162007-01-15 09:50:07PeterWatson152007-01-15 09:49:47PeterWatson142007-01-09 16:00:13PeterWatson132007-01-09 15:59:55PeterWatson122006-12-08 10:20:14PeterWatson112006-12-08 10:19:54PeterWatson102006-12-06 15:40:38PeterWatson92006-12-06 15:40:21PeterWatson82006-12-06 15:23:18PeterWatson72006-12-06 15:22:58PeterWatson62006-12-06 13:00:36PeterWatson52006-12-06 13:00:15PeterWatson42006-12-06 12:59:07PeterWatson32006-08-31 10:41:51PeterWatson22006-08-31 10:35:32PeterWatson12006-08-31 10:33:35PeterWatsonThis program uses Cohen's d as the effect size as recommended by Dunlop, W. P., Cortina, J. M., Vaslow, J. B., & Burke, M. J. (1996) for a paired t-test. This is the same as Cohen's d for a unpaired t-test when the correlation between groups, rho, is zero. Alpha is the (two-tailed) type I error, mdiff is the difference in group means, sd is the average group standard deviation with (common group) power, power, and the correlation between groups equal to rho. The program then outputs the sample size required per group. Computations can also be done using a spreadsheet orin R. You can specify input in terms of Cohen's d. Reference: Dunlop, W. P., Cortina, J. M., Vaslow, J. B., & Burke, M. J. (1996). Meta-analysis of experiments with matched groups or repeated measures designs. Psychological Methods, 1, 170-177. [COPY AND PASTE THE SYNTAX BELOW INTO A SPSS SYNTAX WINDOW AND RUN; ADJUST DATA INPUT VALUES AS REQUIRED] In R we need just one line: For an average paired difference (delta) of 0.2, a difference s.d. (sd) of 1, a power of 0.8 and a two-sided type I error (sig.level) of 0.05 we find that 199 pairs are needed.