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We have two samples with different sizes: 42 and 47 and we have to verify if the means of the two samples are equals. For verify this with t-test, we should verify first if the variances are different or equal with F-test?

Math Info
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    Better to use the Welch-type version of the t-test than use an F-test on the variance. However those sample sizes are reasonably close so moderate differences in the relative variances shouldn't be all that much of a problem. I'm pretty sure this has been answered before. – Glen_b May 10 '17 at 12:41
  • @Glen_b , when I use F-test the null hypothesis is rejected. – Math Info May 10 '17 at 12:48
  • How does that change the advice to do something else without even looking at the F-test? The problem with what you're doing arises because you will change your actions with the t-test based on looking at that F-test. Better not to look at all; if you're not comfortable that the t won't be badly affected you should have just done the Welch test in the first place. – Glen_b May 10 '17 at 12:55
  • Besides the indicated post this was closed as a duplicate of, also see the discussion inside the relevant section of the answer here, and the extended discussion here – Glen_b May 10 '17 at 13:07

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