Provides answers to commonly asked questions about COBRA. Health Benefits Under the Consolidated Omnibus Budget Reconciliation Act (COBRA) (PDF) Provides a detailed overview of the major provisions of COBRA.
In the two-sample pooled t-test the pooled variance is computed by averaging the two individual sample variances. The assumptions for the two-sample pooled t-test for the difference in two means are that there are random samples from two independent normal populations with common but unknown variance.
A t-test can be used to account for the uncertainty in the sample variance when the sample size is small and the data are exactly normal. There is no universal constant at which the sample size is generally considered large enough to justify use of the plug-in test. Typical rules of thumb range from 20 to 50 samples. For larger sample sizes, the t-test procedure gives almost identical p-values as the Z-test procedure. Other location tests that can be performed as Z-tests are the two-sample location test and the paired difference test.