# Thread: Power of a test

1. ## Power of a test

Hi, could someone please explain to me whether the power of a statistical test is the probability that the alternative hypothesis is true?

I know that the power of the test is the probability of a false null hypothesis being rejected but what about the probability that a false null hypothesis is accepted (beta)...? If the alternative hypothesis is true isn;t there a possibilitiy of a type II error...?

thanks

2. Originally Posted by star_Asia
Hi, could someone please explain to me whether the power of a statistical test is the probability that the alternative hypothesis is true?

I know that the power of the test is the probability of a false null hypothesis being rejected but what about the probability that a false null hypothesis is accepted (beta)...? If the alternative hypothesis is true isn;t there a possibilitiy of a type II error...?

thanks
All sorts of things can happen if you don't have a exhaustive list of possibilities.
But the power of the test is as it is defined.

Also classical statistical tests never tell you the probability that a hypothesis
is true, they are always about the likelyhood of the data under the hypothesis,
and accepting/rejecting hypotheses on the basis of such likelyhoods.

RonL

RonL