From Wikipedia:

Cronbach's α (alpha) is a quantity defined in multivariate statistics. It has an important use as measure of the reliability of a psychometric instrument, since it assesses the extent to which a set of test items can be treated as measuring a single latent variable. It was first named as alpha by Cronbach (1951), although an earlier version is 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.

Given that a sample was measured on a set of k items, Cronbach's α is defined as the mean correlation across the items, adjusted upward by the Spearman-Brown prophecy formula by k. It is related to the outcome of an ANOVA of the item data into variance due to the individuals in the sample and variance due to the items...

This makes as much sense to me as arcane Ukrainian lore. Somebody just shoot me.

Filed under: Education, Statistics