Original articleRasch Analysis Reveals Problems with Multiplicative Scoring in the Macular Disease Quality of Life Questionnaire
Section snippets
Patients and Methods
We recruited 108 patients as part of the noninterventional, prospective WAVE (Lucentis in Wet AMD: Evaluation of Visual Acuity and Quality of Life) trial, a postmarketing survey of ranibizumab for nvAMD conducted in Germany from March 2008 to March 2010.12 Ethics approval was obtained from the Institutional review boards of all participating centers. All patients gave signed informed consent for study participation before enrollment and start of treatment. The study adhered to the tenets of the
Clinical Characteristics
Of the 108 patients, most were female (n = 72; 67%), and the average age was 77 years, with two-thirds of the sample aged >75 years (Table 1). Twenty percent of patients had had prior treatment for nvAMD (photodynamic therapy, laser photocoagulation, intravitreal bevacizumab injections). Mean presenting visual acuity was LogMAR 0.58±0.33 (mean value ± standard deviation). Two thirds of patients were classified as vision impaired (LogMAR >0.05; Table 1).
Discussion
Using Rasch analysis, we have demonstrated that the MacDQoL in its current form fails to meet the criteria of a valid functioning scale. In its multiplicative form, several disordered thresholds beyond repair suggested that respondents were unable to discriminate between the large number of response options required by the MacDQoL. Omitting the importance rating and using the impairment scale only also revealed issues with the response categories. However, after collapsing 2 response categories
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Manuscript no. 2011-1715.
Financial Disclosure(s): The authors have no proprietary or commercial interest in any of the materials discussed in this article.
Funded by the German Research Council grant (DFG FI 1540/5-1) to RPF. CERA receives Operational Infrastructure Support from the Victorian Government. This study was supported by Novartis Pharma GmbH, Germany.