What is coefficient alpha? An examination of theory and applications.

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Abstract
Coefficient alpha (Cronbach, 1951) is certainly one of the most important and pervasive statistics in research involving test construction and use. A review of the Social Sciences Cita- tions Index for the literature from 1966 to 1990 revealed that Cronbach's (1951) article had been cited approximately 60 times per year and in a total of 278 different journals. In addi- tion to the areas of psychology in which one may expect to see alpha used, such as educational, industrial, social, clinical, child, community, and abnormal psychology, this list of jour- nals included representatives from experimental psychology, so- ciology, statistics, medicine, counseling, nursing, economics, political science, criminology, gerontology, broadcasting, an- thropology, and accounting. In spite of its widespread use, how- ever, there is some confusion as to the true meaning and proper interpretation of the statistic. In this article I address this confusion in two ways. First, a theoretical discussion of alpha is presented. This includes some of the many statements that have been made about alpha and an attempt to integrate these statements. Second, I take a more practical approach in which the interpretation of alpha is exam- ined by observing the changes in alpha as the number of items and interitem correlations are manipulated.

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