What conditions must be met for conducting a two-sample t test for the means?
Conditions for conducting two sample t-test for means:
1.) Parent populations from which samples are drawn are normally distributed.
2.) The two samples are random and independent of each other.
3.) Population variances are equal and unknown.
For validity of t-test we should check the equality of variances with the help of F-test for equality of variances. If the hypothesis is rejected then we cannot apply t-test. In such cases we apply Behren's d-test.
But for practical problems the assumptions 1.) and 3.) are taken to be true.