What does Cronbach’s alpha tell us about the EQ-5D? A methodological commentary to “Psychometric properties of the EuroQol Five-Dimensional Questionnaire (EQ-5D-3L) in caregivers of autistic children”

In a paper just accepted for publication in Quality of Life Research, Khanna et al. [1] investigate the psychometric properties of the EQ-5D with three levels [2] using data from a sample of 316 US—American caregivers of autistic children. The authors examine convergent and discriminant validity of the five EQ-5D dimensions by analyzing the relation of these dimensions with the dimensions of the SF-12v2 [3], and they examine known group validity by analyzing how the severity of the children’s autism relates to the EQ-5D index and the VAS scale. With a few exceptions, the results of these examinations accord with the authors’ expectations. The authors interpret this as evidence for the EQ-5D’s validity. The authors also examine the reliability of the EQ-5D. For this purpose, they compute Cronbach’s alpha and item-total correlations for the five dimensions of the EQ-5D. Cronbach’s alpha is only 0.63, whereas the item-total correlations range from 0.25 for anxiety/depression to 0.58 for usual activities. Following the recommendations of Nunnally [4], the authors judge the result for Cronbach’s alpha as unsatisfactory and the results for the item-total correlations as acceptable. …