The construction and validation of the assessment of mental health related quality of life AQoL-8D (PsyQoL) instrument: data

All the AQoL instruments (see aqol.com.au) are utility-weighted generic Qol instruments which means they are able to be widely used and for economic evaluations. The data collection consists of questionnaires, and supporting documentation, including the scoring algorithms. Algorithms analyse instrument data and produce a score for each dimension and a utility score for the instrument overall. Investigators were from Monash University's Centre for Health Economics, University of Melbourne Department of Psychiatry, The Melbourne Clinic and representatives from each of the affiliated mental health services. Mental health is one of the national health priority areas as well as one of the largest contributors to burden of disease. The project goal was to develop a generic instrument to measure quality of life in the area of mental health. While developed originally for assessing the quality of life associated with mental health problems, the instrument can be used across various disease groups such as mental health, cancer, cardiovascular, diabetes, vision and hearing loss, asthma and obesity. The instrument is able to give a utility measure of quality of life of patients before and after receiving health services and is the only instrument to date which was both constructed using correct psychometric principles of instrument construction and which describes health states in terms of the effect upon a patient's ability to function in a social environment (see WHO ‘Handicap’). As a generic instrument, it can be applied to many settings. A representative sample of members of the public (n=200 randomly selected) and mental health patients at various Melbourne mental health centres (n=470) were recruited to complete a 140-item Construction Item Bank. Exploratory Factor Analysis followed and Structural Equation Modelling of item responses to produce the final 35 item 8 dimension AQoL-8D instrument. A further 300 members of the public and an equal number of patients attended face to face Time Trade Off interviews involving 370 health state scenarios to derive the preference or utility weights, or tariffs. Participants were all between 18 and 65 years of age, and Australian residents.