Metric properties of the MacDQoL, individualized macular-disease-specific quality of life instrument, and newly identified subscales in French, German, Italian, and American populations

Objectives: The aims of this analysis were to confirm the UK results in other countries and to explore the possibility of subscales of the 25-Item Macular disease Dependent Quality of Life (MacDQoL) questionnaire. Methods: Two clinical studies were pooled. Principal components analyses (Varimax) were conducted on baseline data from each country and from all combined. Factorial structures were compared between countries, and Cronbach alpha values were used to identify item clusters. Four groups of patients were created according to visual acuity (VA) in the best eye (BE < 10/20; BE >= 10/20) and worst eye (WE < 10/100; WE >= 10/100). These groups were used to investigate (analysis of variance) the sensitivity of MacDQoL to VA impairment and to compare it with the NEI-VFQ-25 generic visual function questionnaire. Results: A total of 797 patients (mean age 76.8 years; 55.8% women) had wet age-related macular degeneration (AMD). Strong correlations between the MacDQoL items (r > 0.48) and factor loadings > 0.49 on a forced one-factor analysis supported the use of an average weighted impact score. Four constructs (Cronbach alpha > 0.8) were derived, represented by the labels: Essential tasks, Family/social life, Activities/capabilities, and Embarrassment. The structure did not differ among the four countries involved, except one item (Finance), which has been excluded. Patients with BE VA < 10/20 and WE VA < 10/100 produced significantly worse overall scores than those with BE VA > 10/20 and WE VA > 10/100 (MacDQoL P > 0.0001; NEI-VFQ-25 P < 0.0001). Conclusions: The analysis confirmed the metric properties of the MacDQoL. The MacDQoL offers a broad individualized measure of the impact of MD on quality of life. Copyright (C) 2011, International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc.