Mokken scaling of the Myocardial Infarction Dimensional Assessment Scale (MIDAS)

Aims The purpose of this study was to examine the hierarchical and cumulative nature of the 35 items of the Myocardial Infarction Dimensional Assessment Scale (MIDAS), a disease-specific health-related quality of life measure. Method Data from 668 participants who completed the MIDAS were analysed using the Mokken Scaling Procedure, which is a computer program that searches polychotomous data for hierarchical and cumulative scales on the basis of a range of diagnostic criteria. Results Fourteen MIDAS items were retained in a Mokken scale and these items included physical activity, insecurity, emotional reaction and dependency items but excluded items related to diet, medication or side-effects. Item difficulty, in item response theory terms, ran from physical activity items (low difficulty) to insecurity, suggesting that the most severe quality of life effect of myocardial infarction is loneliness and isolation. Conclusions Items from the MIDAS form a strong and reliable Mokken scale, which provides new insight into the relationship between items in the MIDAS and the measurement of quality of life after myocardial infarction.