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Let's consider two groups, 150 and 15, with variability in each group, say an SD of 2. Let's look at the power of a "not significant" t test result at significance level (alpha) = 0.05 (two-tailed) Choose the smallest difference between the means that you think might be interesting or important, and read the power of the trial to detect that difference. <NOBR Power (%) 2.37 99 1.99 95 1.79 90 1.66 85 1.55 80 1.46 75 1.37 70 1.22 60 1.08 50 0.94 40 0.79 30 Regards, Stan Alekman In a message dated 11/14/2009 7:11:54 A.M. Eastern Standard Time, [log in to unmask] writes: Dear All I have two groups named Middle Managers (MM) and Top Managers (TM) and I want to test whether the mean differences between the two are significant or not. My issue is that Group 1 (MM) has 150 respondents (10 respondents from one organization each) while Group 2 (TM) has 15 respondents (One response from each organization- Because Top Managers are fewer in numbers in a given organization) I plan to use T-test for testing the significance but am worried about the disparity between sample size of the two groups...The data has already been collected...Do I need to increase the sample size? Would welcome any advice/suggestions in this regard... -- Dr. Bilal Mustafa Khan Assistant Professor Department of Business Administration Aligarh Muslim University (AMU) India 0091-9897310838