The dimensional structure of the MacNew Health Related Quality of Life questionnaire: A Mokken Scale Analysis.

OBJECTIVE The MacNew Health related Quality of Life Questionnaire is a widely used instrument for the assessment of health related quality of life in cardiac patients. The study addresses for the first time the dimensional structure of the MacNew with Mokken Scale Analysis (MSA). METHODS Separate exploratory MSA of the MacNew was conducted in a large Spanish (n=1012) and a medium sized Austrian sample (n=262) of patients with Coronary Artery Disease (CAD) after Percutaneous Coronary Intervention (PCI). The results of both samples were summarized in a synthesis model. Confirmatory MSA and Confirmatory Factor Analysis (CFA) were used to evaluate the model. RESULTS The synthesis model comprises 21 items forming a unidimensional sum scale of moderate strength. On the level of subdomains we define two strong unidimensional subscales (restriction: 6 items, and emotional: 10 items) and two smaller item sets (symptoms: 2 items and social: 3 items). 5 items were excluded due to low scalability in both samples. CONCLUSION Our results generally support the use of the MacNew Global score, with the limitation, that five items may be questionable with regard to scalability. On the level of unidimensional subscales MSA suggests to differentiate between a six-item restriction scale and a ten-item emotional scale. The study demonstrates that Mokken Scale Analysis complements the results of factor analysis and can contribute to a more comprehensive understanding of the dimensional structure of Health-related Quality of Life questionnaires.