Question

In most situations, the researcher usually has a hunch about the direction of the difference between the populations being compared. But most researchers still opt to perform a two-tailed (non-directional) test instead of a one-tailed (directional) test. What might be the rationale for this?

Answer 1

yes, in most cases the researcher has an idea about the direction of the difference between the populations being compared and still they use the two tailed hypothesis as compared to one tailed hypothesis test.

The reason for selecting the two tailed hypothesis testing over the one tailed hypothesis testing is that the two tailed hypothesis testing allows the researcher to test the condition in both directions whereas one tailed hypothesis allows to test only in one direction.

Suppose we are testing the hypothesis for left tailed and it is not significant, but it is significant for right tailed. In this case, there is a relationship between the variables using two tailed hypothesis but no relationship using one tailed hypothesis, that's the reason why most researchers still opt to perform a two tailed hypothesis test instead of one tailed test.