Reliability and validity of a single item measure of quality of life scale for adult patients with cystic fibrosis

Background: It is important to monitor health related quality of life in order to determine the efficacy of interventions and physical functioning of patients with cystic fibrosis in their daily activities. There is no a single-item global quality of life scale for routine clinical practice for adult patients with cystic fibrosis. We assessed the reliability and validity of a single-item global quality of life scale and compared with the Cystic Fibrosis Quality of Life Questionnaire (CF-QOL) for adult patients with cystic fibrosis. Method: 121 (men = 66, women = 55) adult cystic fibrosis patients self-completed the CF-QOL, the Hospital Anxiety Depression Scale, and the single item global quality of life scale at the out patient clinic. 33 (17 women) completed the repeat questionnaires at home within two weeks. Socio-demographic characteristic and lung function data were extracted from the recent medical notes. Results: Mean (SD) age was 29.6 (8.9) years and mean (SD) forced expiratory volume in 1 second was 2.20 (0.94) litres. The test-retest reproducibility using the intra-class correlation coefficient (ICC) for the CF-QOL was 0.83, 95% confidence interval 0.68 to 0.91. The single item global quality of life ICC score was 0.78, 95% confidence interval 0.59 to 0.88. Concurrent validity of the single-item global quality of life was examined in relation to all items of the CF-QOL, frequent episodes of readmission, anxiety and depression (all, p < 0.01) were moderately correlated. Conclusion: The study provides preliminary evidence that the single-item quality of life scale is acceptable, valid and repeatable for adult patients with cystic fibrosis. It is a promising tool that can be easily incorporated into a routine clinical practice to assess patients' quality of life.