Cronbach’s alpha is one of the worst internal consistency estimators: a simulation study
Cronbach’s alpha is the most common internal consistency index in educational sciences. The goal of this article is to assess the performance of six internal consistency estimators by conducting a simulation study. The simulation focuses on Cronbach’s alpha, lambda-2, Guttman’s lambda-4 and lambda-6, the greatest lower bound (GLB) and the omega. Forty-five scenarios were defined by the sample size, the number of items and the value of factorial saturation coefficients. The results suggest that if the instrument has five items, the preferred estimator would be omega. In other cases, it would be the GLB. Alpha and lambda-2 are systematically the two estimators that most underestimate the value of internal consistency and should be avoided. Lambda-6 would be the best estimator offered by SPSS. Overall, this study offers an empirical rationale for a change of practice in educational research.