In the context of educational measurement, a power test usually refers to a measurement tool composed of several items and applied without a relevant time limit. The respondents have a very long time, or even unlimited time, to solve each of the items, so they can usually attempt all of them. The total score is often computed as the number of items correctly answered, and individual differences in the scores are attributed to differences in the ability under assessment, not to differences in basic cognitive abilities such as processing speed or reaction time. This entry describes what a power test is and how it should be applied, provides some examples of power tests, and explains how it is related to the concept of test speediness.