Statistics? How to tell if it is a one tail or two tailed test?

Question

How do you tell in a stats problem if it is a right tailed, left tailed, or two tailed test?

Answer 1

If your hypothesis is that the two groups are not equal, then use a two-tailed test. If your hypothesis is that group A is larger (has a greater mean, for instance) than the control or group B, use a one-tailed (right) test. If your hypothesis is that group A is smaller, use a one-tailed (left) test.