Social science measurement requires scores that are both valid and reliable. Reliability refers to the amount of random fluctuation in a set of scores. One of the most popular methods for estimating the reliability of test scores is coefficient α, which estimates the proportion of observed score variance that is due to true score variance. The coefficient α is widely used in the education and [Page 303]psychosocial literature as an index of reliability of test scores.

Coefficient α was first described by Lee Cronbach in 1951, so it is sometimes termed Cronbach’s α. Coefficient α is used for establishing reliability of test scores from a single administration. However, in spite of the common use of coefficient α in the literature as an index of reliability of ...