In testing the difference between the means of two normally distributed populations, the number of degrees of freedom associated with the unequal-variances t-test statistic usually results in a non-integer number. It is recommended that you: A) round up to the nearest integer. B) round down to the nearest integer. C) change the sample sizes until the number of degrees of freedom becomes an integer. D) assume that the population variances are equal, and then use df = n₁ + n₂ - 2.

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It is recommended to round the number of degrees of freedom down to the nearest integer in order to select the appropriate critical values for the t-test. This conservatively estimates the variability in the data and reduces the chances of making a Type I error (rejecting the null hypothesis when it is actually true).

In Testing the Difference Between the Means of Two Normally