when do we use two sample t test
Student's t-test Two-sample t-tests for a difference in mean involve independent samples or unpaired samples. Paired t-tests are a form of blocking, and have greater power than unpaired tests when the paired units are similar with respect to "noise factors" that are independent of membership in the two groups being compared.[12] In a different context, paired t-tests can be used to reduce the effects of confounding factors in an observational study.