Variability of Coefficient Alpha: An Empirical Investigation of the Scales of Psychological Wellbeing
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abstract
Using reliability generalization analysis, the purpose of this study was to characterize the average score reliability, the variability of the score reliability estimates, and explore possible characteristics (e.g., sample size) that influence the reliability of scores across studies using the Scales of Psychological Wellbeing (PWB; Ryff, 1989 , 2014 ). Published studies were included in this investigation if they appeared in a peer-reviewed journal, used 1 or more PWB subscales, estimated coefficient alpha value(s) for the PWB subscale(s), and were written in English. Of the 924 articles generated by the search strategy, a total of 264 were included in the final sample for meta-analysis. The average value reported for coefficient alpha referencing the composite PWB Scale was 0.858, with mean coefficient alphas ranging from 0.722 for the autonomy subscale to 0.801 for the self-acceptance subscale. The 95% prediction intervals ranged from [.653, .996] for the composite PWB. The lower bound of the prediction intervals for specific subscales were >.350. Moderator analyses revealed significant differences in score reliability estimates across select sample and test characteristics. Most notably, R2values linked with test length ranged from 40% to 71%. Concerns were identified with the use of the 3-item per PWB subscale which reinforces claims advanced by Ryff (2014) . Suggestions for researchers using the PWB are advanced which span measurement considerations and standards of reporting. Psychological researchers who calculate score reliability estimates within their own work should recognize the implications of alpha coefficient values on validity, null hypothesis significant testing, and effect sizes.
