Objective: The purpose of this study was to assess the reliability and validity of the Diabetes Diet-Related Quality-of-Life (DDRQOL) scale, which is a measure of the influence of diet therapy on patients' quality of life (QOL).
Research design and methods: Patients with type 2 diabetes (n = 236) who were being treated on an outpatient basis were asked to complete the self-administered DDRQOL instrument. The factor validity, convergent and discriminant validity, internal consistency, and reproducibility of the DDRQOL scale were then assessed. Spearman's rank correlation coefficients among the DDRQOL scale and each of the SF-36 subscale scores were calculated to evaluate its convergent and discriminant validity.
Results: Based on the results of the factor analysis, the following seven subscales were adopted for the DDRQOL: "satisfaction with diet," "burden of diet therapy," "perceived merits of diet therapy," "general perception of diet," "restriction of social functions," "vitality," and "mental health." As hypothesized, the DDRQOL scale was associated with each of the SF-36 subscales, with convergent and discriminant validity being generally exhibited. Cronbach's alpha-coefficient was between 0.71 and 0.84, suggesting strong internal consistency. The intraclass correlation coefficient of the subscales, with the results of a test-retest conducted 2 weeks later, was between 0.46 and 0.75, suggesting some degree of reproducibility.
Conclusions: These findings indicate that the DDRQOL scale has a reasonable degree of reliability and validity, and its application for the assessment of the needs of a patient's diet and the evaluation of diet education with regard to QOL is awaited.