What is a one-tailed test?

A one-tailed test is defined as a hypothesis test that considers values in only one direction away from the null hypothesis. This means that when setting up the test, researchers are interested in determining whether there is a significant effect or difference in a specific direction, such as greater than or less than a particular value, rather than merely identifying any difference at all.

In a one-tailed test, for instance, a researcher might hypothesize that a new treatment will result in an increase in scores compared to a placebo. The analysis will focus solely on whether the treatment yields higher scores, not on the possibility of lower scores. This focus on one direction allows for more statistical power to detect an effect if it exists, as the critical region for significance is concentrated in one tail of the distribution.

The other options represent different concepts in statistical testing. A two-tailed test would consider values in both directions away from the null hypothesis, allowing detection of effects in either direction. The other choices describe methods of comparison applicable in specific contexts but do not capture the essence of what a one-tailed test is designed to evaluate.