Estimation of a Preference-based Index For Asthma From The Asthma Quality of Life Questionnaire (AQL-5D)
This project derived a preference-based measure for asthma from the Asthma Quality of Life Questionnaire (AQLQ). This measure enables AQLQ data to be used to generate utility values for use in economic evaluation.
The AQLQ is a 32-item questionnaire and cannot be used in economic evaluation as its scoring is not preference-based. The large number of items means that the AQLQ is too large to be amenable to valuation in its current format. This project applied Rasch models to samples of responders to the AQLQ with the aim of selecting a subset of items for a classification system that is amenable to valuation. Selection of items for the classification system was also informed by classical psychometric criteria for item selection (feasibility, internal consistency, floor and ceiling effects, and responsiveness).
A classification system was developed with 5 dimensions: concern, short of breath, weather and pollution, sleep, and activities. Each dimension has 5 levels of severity and the classification system overall describes 3125 states.
A valuation study was conducted using the time trade-off elicitation technique on a random sample of the UK general population. A sample of 307 respondents valued 99 asthma health states selected from the AQL-5D. Regression models were estimated to predict utility values for all possible 3125 health states defined by the AQL-5D, and the models were compared in terms of their ability to predict mean values for the 99 states. The worst state defined by the classification system has a utility value of 0.459 and the best state has a value of 1, anchored onto the full health-dead 1-0 scale.
- Yang Y, Brazier J, Tsuchiya A, Young T. Estimating a Preference-Based Index for a 5-Dimensional Health State Classification for Asthma Derived From the Asthma Quality of Life Questionnaire Medical Decision Making [forthcoming].
- Young TA, Yang Y, Brazier JE, Tsuchiya A The Use of Rasch Analysis in Reducing a Large Condition-Specific Instrument for Preference Valuation: The Case of Moving from AQLQ to AQL-5D. Medical Decision Making [forthcoming].