Cronbach's α (alpha) is a statistic. It has an important use as a measure of the reliability of a psychometric instrument. It was first name as alpha by Cronbach (1951), as he had intended to continue with further instruments. It is the extension of an earlier version, the Kuder-Richardson Formula 20 (often shortened to KR-20), which is the equivalent for dichotomous items, and Guttman (1945) developed the same quantity under the name lambda-2.