Objective: To examine the effects of type I and type II diabetes on patient perceptions of their quality of life and compare the psychometric properties of a generic versus a diabetes-specific quality of life measure.
Research design and methods: Consecutive outpatients (n = 240) from a large multispecialty diabetes clinic were studied on a single occasion using two measures of quality of life--Diabetes Quality of Life Measure (DQOL) and the Medical Outcome Study Health Survey 36-Item Short Form (SF-36). No interventions were performed. This study examines three issues: 1) the reliability (internal consistency) of the two measures; 2) the relationship between the DQOL and SF-36 scales; and 3) the influence of clinical patient characteristics, such as number and severity of diabetes complications, on quality of life. Examination of this issue provides information about the construct validity of the two quality of life measures.
Results: The estimates of internal consistency (Cronbach's alpha) for the DQOL and SF-36 subscales ranged from 0.47 to 0.97. These values were very similar to the published findings from previous studies. The subscales of the two measures were variably correlated with one another (range of correlations: -0.003 to 0.60), indicating that the areas of functioning addressed by the DQOL and SF-36 overlapped only to a modest degree. Examination of the relationship of demographic factors to the DQOL measures suggests that they are not generally confounded by factors such as education, sex, or duration of diabetes. Health-related quality of life is affected by the marital status of both type I and type II diabetic patients, with separated and divorced individuals generally experiencing lower levels of quality of life. The quality of life measures were sensitive to clinical characteristics, such as frequency and severity of complications. Even after factors such as marital status and, among type II diabetic patients, type of treatment, patients' severity of diabetes complications was a significant predictor of both the diabetes-related and the more broad-based measure of quality of life. For type II diabetic patients, insulin treatment was associated with lower levels of satisfaction with diabetes and greater impact of diabetes on quality of life.
Conclusions: This study provides evidence for the reliability and validity of two measures of quality of life. The two measures examine quality of life from different but complimentary perspectives. The DQOL seems more sensitive to lifestyle issues and contains special questions and worry scales oriented toward younger patients, whereas the SF-36 provides more information about functional health status. Thus, the measures may be used usefully in combination in studies of both type I and type II diabetic patients.