Alternative Hypothesis

An alternative hypothesis is one in which a difference (or an effect) between two or more variables is [Page 19]anticipated by the researchers; that is, the observed pattern of the data is not due to a chance occurrence. This follows from the tenets of science, in which empirical evidence must be found to refute the null hypothesis before one can claim support for an alternative hypothesis (i.e. there is in fact a reliable difference or effect in whatever is being studied). The concept of the alternative hypothesis is a central part of formal hypothesis testing.

Alternative hypotheses can be nondirectional or directional. If nondirectional, an alternative hypothesis is tested with a two-tailed statistical test and is stated in words to the effect that "A differs from ...