The Assessment of Quality of Life (AQoL) II Instrument: Overview and creation of the utility scoring algorithm

MAU instruments seek to measure the ‘utility’ of health states in a way suitable for use in economic evaluation studies and, in particular, cost utility analysis (CUA). The Assessment of Quality of Life, Mark 2 (AQoL 2) project was undertaken specifically to increase the sensitivity of measurement in the region of full health, where most other instruments, including the earlier AQoL 1 instrument are relatively insensitive. In sum, the AQoL 2 instrument estimates utility using a three stage procedure. Items are (i) weighted and combined using a multiplicative model to obtain dimension scores; (ii) these are similarly weighted and combined to obtain an initial AQoL score; (iii) this is then transformed econometrically to produce the final estimate of a health state utility. As with AQoL 1 the research program also sought to experiment with new methods for achieving this. AQoL 1 was the first instrument to use a multi level descriptive system with five dimensions of health separately modelled and then combined. After experimentation it incorporated a new way of modelling the utility of health states worse than death. AQoL 2 adopted this same multi level structure It was developed in 2 stages. The first used a series of confirmatory factor analysis using Lisrel, to construct dimension models. The second was a confirmatory factor (SEM) analysis of the overall AQoL which combined all of the dimensions. Utility scores were modelled in three stages. Time trade-off (TTO) importance weights were first combined into dimensions and to the dimensions into a single score using multiplicative (non stochastic) models (as with AQoL 1). However these were subsequently adjusted in a third stage econometric ‘correction’ based upon independently collected multi attribute – TTO – scores.