What does it mean when variance is unequal?
For the unequal variance t test, the null hypothesis is that the two population means are the same but the two population variances may differ. The unequal variance t test reports a confidence interval for the difference between two means that is usable even if the standard deviations differ.
How do you know if the variances are the same?
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 to determine equal or unequal variance in t tests?
1. Use the Variance Rule of Thumb. As a rule of thumb, if the ratio of the larger variance to the smaller variance is less than 4 then we can assume the variances are approximately equal and use the Student’s t-test. Sample 1 has a variance of 24.86 and sample 2 has a variance of 15.76.
How to do two independent sample unequal variance?
Two Independent Samples Unequal Variance (Welch’s Test) To conduct a two independent sample comparison of means test, you follow very similar steps as described in the one sample test with some modifications. For this problem, we want to compare the average weights of blue crabs in two river basins: (1) Tar-Pamlico and (2) Neuse River.
What do equal variances and unequal variances mean in stattools?
“Equal Variances” and “Unequal Variances” in Two-Sample Inferences In StatTools, I’m selecting a confidence interval or hypothesis test about the difference in means of two independent samples. StatTools gives two columns of results, headed “Equal Variances” and “Unequal Variances”. What do those mean?
Which is correct equal variances or unequal variances?
Finally, even after you go through all that, pooling or not (“Equal Variances” column or “Unequal Variances” column in StatTools results) usually makes only a minor difference. The conservative choice is to use the “Unequal Variances” column, meaning that the data sets are not pooled.