When to use two sample assuming equal variances?
t-Test: Two-Sample Assuming Equal Variances. This test does not assume that the variances of both populations are equal. Paired t-tests are typically used to test the means of a population before and after some treatment, i.e. two samples of math scores from students before and after a lesson.
How to do a two sample t test?
Uncheck Labels since we did not include the column headings in our Variable 1 and 2 Ranges. Keep the Alpha = 0.05. Enter D1 for the Output Range. Click OK. Cells E4 and F4 contain the mean of each sample, Variable 1 = Beginning and Variable 2 = End.
What is the one tail of the t test?
If t < 0, P (T <= t) one-tail is the probability that a value of the t-Statistic woulbe observed that is more negative than t. If t >0, P (T<=t) one tail is the probability that a value of the t-Statistic would be observed that is more positive than t.
What does p ( t < 0 ) one tail mean?
If t >0, P (T<=t) one tail is the probability that a value of the t-Statistic would be observed that is more positive than t. P (T <=t) two tail is the probability that a value of the t-Statistic would be observed that is larger in absolute value than t.
Why do we need to test for unequal variances?
Because the susceptibility of different procedures to unequal variances varies greatly, so does the need to do a test for equal variances. For example, ANOVA inferences are only slightly affected by inequality of variance if the model contains only fixed factors and has equal or almost equal sample sizes.
How to test if two populations are equal?
Purpose: Test if variances from two populations are equal . An F-test (Snedecor and Cochran, 1983) is used to test if the variances of two populations are equal. This test can be a two-tailed test or a one-tailed test. The two-tailed version tests against the alternative that the variances are not equal.
How are Anova inferences affected by inequality of variance?
For example, ANOVA inferences are only slightly affected by inequality of variance if the model contains only fixed factors and has equal or almost equal sample sizes. Alternatively, ANOVA models with random effects and/or unequal sample sizes could be substantially affected.