What is meant by a one-sided/two-sided hypothesis test? Is it just another term for a one-tailed/two-tailed hypothesis test?
And is a hypothesis test necessarily either one-tailed or two-tailed, or it could be neither?
Cross Validated is a question and answer site for people interested in statistics, machine learning, data analysis, data mining, and data visualization. It only takes a minute to sign up.Sign up to join this community
For a one sided test you are only interested in results in one direction and conversely for two sided. For many tests this corresponds to using one or two tails of the reference distribution of the test statistic. However there are situations where the two sided test only uses one tail so people have come to use the term sided rather than tail. In practice confusion is unlikely
What you refer to as non sided is what happens in situation like the comparison of multiple groups, goodness of fit, and many others. In those cases it does not make sense to speak of a direction of difference. For instance if you compare three means all you can say is that they are different or not.