Abstract
The focus of this commentary is on the attempt to create EQ-5D-3L ordinal preferences from a disease specific asthma questionnaire, the Asthma Quality of Life Questionnaire (AQLQ). The question is whether it is possible from the perspective of fundamental measurement to create a simple linear algorithm to map AQLQ scores to EQ-5D-3L preferences. It is proposed that this is mathematically impossible as the aggregate AQLQ score is ordinal, apart from the fact that the AQLQ is a multiattribute score that lacks construct validity and any pretense to having interval properties. Disallowing the mapped utilities means that the modelling cannot be sustained. It is proposed that the focus should be on single attribute measures of the latent construct "need fulfillment quality of life". These measures would meet the required standards of Rasch Measurement Theory (RMT) applying simultaneous conjoint standards of measurement theory, as well as capturing the patient voice.
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