Comparison of SF-36 and WHOQoL-BREF in Measuring Quality of Life in Patients with Type 2 Diabetes

Objective: This study aimed to compare the quality of life (QoL) in patients with type 2 diabetes using two WHOQoL -BREF and SF-36 questionnaires in Iran. Patients and Methods: In this cross-sectional study, 1847 patients with type 2 diabetes were recruited from rural health-care centers affiliated to Neyshabur County (Iran) in 2012. In addition to demographic information, two questionnaires WHOQoL-BREF and SF-36 questionnaires were used for data collection. Cronbach's alpha coefficient was used for scale reliability. We conducted an exploratory factor analysis for the investigation of construct validity. Convergent and discriminant validity were analyzed using Spearman correlation coefficient. To determine the relationships between the eight domains of SF-36 and four domains of the WHOQoL-BREF, structural equation modelling was performed. Results: Cronbach's alpha coefficients were acceptable for all domains of both WHOQoL-BREF (0.69-0.86) and SF-36 (0.63-0.92) questionnaires. The principal component analysis showed two separate factors: one for all domains of SF-36 and another for all domains of WHOQoL-BREF. Spearman correlation coefficients of both instruments were partly to strongly correlated with most domains (r >= 0.40). Correlations for domains with similar constructs were stronger than those measuring varied constructs. Structural equation modelling recommended approximately moderate relationships among the SF-36 and WHOQoL-BREF domains. Conclusion: Our study suggests that SF-36 and WHOQoL-BREF are reliable instruments for clinical and research uses, respectably. However, results of the goodness of fit showed that the WHOQoL-BREF was fitted well. Also, the WHOQoL-BREF can be considered more suitable for the study population.