Measurement Reliability in Psychology: Method Development, Infatuation with Cronbach’s Alpha Coefficient, and Recommendations for Appropriate Reliability Estimation
Keywords:psychometrics, measurement reliability, Cronbach’s alpha, McDonald’s omega, test theory, structural equation modelling
AbstractThe purpose of this review article is to indicate the abundant history of the concept of measurement reliability and steep improvement in reliability estimation since the 1940s, which produced a large number of approaches to its estimation. At the beginning of the article, a brief historical review of the emergence of the concept of measurement reliability together with methods of reliability estimation is given. Afterwards, different coefficients of internal consistency are described in chronological order. Application of Cronbach’s α coefficient without verifying necessary assumptions is criticized, and common misconceptions about α coefficient are elucidated. Necessary assumptions for use of Cronbach’s α coefficient, its biases in case of unfulfilled assumptions, best practice of reporting, and potential applications of the coefficient beside reliability estimation are outlined. However, necessary assumptions extremely rarely hold in practice and application of some other coefficients is often more appropriate, such as λ2, λ4, ρGLB or ω, the least biased one in most cases. Guidelines for use of mentioned coefficients are offered. The most recent approach to reliability estimation is by using structural equation modelling due to its ability to conveniently assess aforementioned assumptions and its synergy with ω and ωH coefficients, as well as its appropriateness in case of complex measurement models. Finally, conceptual issues on measurement reliability are discussed and guidelines for further research of measurement reliability are suggested.