Construction of the descriptive system for the assessment of quality of life AQoL-6D utility instrument

The AQoL program introduced the use of psychometric methods in the construction of health related MAU instruments. To develop the AQoL-6D we selected 112 items from previous research, focus groups and expert judgment and administered them to 316 members of the public and 302 hospital patients. The search for content validity across a broad spectrum of health states required both formative and reflective modelling. We employed Exploratory Factor Analysis and Structural Equation Modelling (SEM) to meet these dual requirements.The resulting instrument employs 20 items in a multi-tier descriptive system. Latent dimension variables achieve sensitive descriptions of 6 dimensions which, in turn, combine to form a single latent QoL variable. Diagnostic statistics from the SEM analysis are exceptionally good and confirm the hypothesised structure of the model.The AQoL-6D descriptive system has good psychometric properties. They imply that the instrument has achieved construct validity and provides a sensitive description of HRQoL. This means that it may be used with confidence for measuring health related quality of life and that it is a suitable basis for modelling utilities for inclusion in the economic evaluation of health programs.Health related Multi-Attribute Utility (MAU) instruments seek to measure the quality of life (QoL) of individuals in a way which allows its inclusion in economic evaluation studies and, in particular, Cost Utility Analyses (CUA). While their defining characteristic is the creation of an index of utility (or strength of preference) they may also be used, like non-utility generic instruments such as the SF-36, to measure health related quality of life (HRQoL) or to provide health profiles. Construction of an MAU instrument involves two tasks: creating a descriptive system - a set of questions whose answers describe a person's health state - and devising a scoring formula, which combines and reduces the answers to a single number which seeks to me