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Chapter 9. Comparing Two Means > 9.2 Two-Sample t-Test

9.2 Two-Sample t-Test

The two-sample t-test is used to test the difference between the means of two normally distributed populations. The two-sample t-test requires several assumptions:

  • The two samples of size nA and nB are independent. This usually means that subjects or test specimens are randomly assigned to one of the two treatment groups. If that is not possible, they should be at least randomly selected from the populations whose means are to be compared.

  • The order in which subjects or specimens are tested is random.

  • The variances of the two populations are equal. If they are unequal, a different procedure needs to be used.


  

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