Page "Null hypothesis" Paragraph 30

An example of a one-tailed null hypothesis would be that, in a medical context, an existing treatment, A, is no worse than a new treatment, B.

The corresponding alternative hypothesis would be that B is better than A.

Here if the null hypothesis weren't rejected ( i. e. there is no reason to reject the hypothesis that A is at least as good as B ), the conclusion would be that treatment A should continue to be used.

If the null hypothesis were rejected, i. e. there is evidence that B is better than A, the result would be that treatment B would be used in future.

An appropriate hypothesis test would look for evidence that B is better than A, not for evidence that the outcomes of treatments A and B are different.

Formulating the hypothesis as a " better than " comparison is said to give the hypothesis directionality.