In principle each MAU instrument purports to measure the ‘utility’ of a health state; that is, each purports to measure the strength of a person’s preference for that health state. Consequently, the numbers produced by instruments should be the same. In practice they differ very significantly. Drawing upon results from 7720 respondents the ‘Multi Instrument Comparison’ (MIC) project has demonstrated that different instruments are sensitive to different dimensions or facets of a health state. The EQ-5D primarily measures physical function and pain. The AQoL-8D largely measures psycho-social facets to which the EQ-5D is relatively insensitive. The MIC research papers provide pairwise comparisons of all MAU instruments and quantifies their responsiveness to different dimensions of the QoL (see Richardson, Iezzi, Khan, Maxwell 2012 A cross-national comparison of 12 quality of life instruments, MIC Paper 2: Australia Research Paper 78, CHE Monash University. Results for UK, USA, Canada and Norway are in subsequent reports).

The short answer is ‘no, not if the measurement of QoL – 50 percent of the QALY equation – is of importance.

The longest AQoL instrument – AQoL-8D – takes an average of 5.5 minutes to complete in its online version. (Of course some people will take longer.) A common comment is that clinicians are reluctant to include MAU questions in their already large battery of questionnaires. There is, however, some responsibility upon consultant economists to maintain the quality of the advice and service provided. If an instrument is insensitive to a health intervention – as a number of MAU instruments are to psycho-social interventions – then the ‘price’ of compromising with respect to the instrument may be an invalid evaluation, a high cost to QALY ratio and the failure of the intervention to be funded. There is, in fact, very limited evidence on patient resistance to relatively short questionnaires as demonstrated by the Multi Instrument Comparison (MIC) project where 7720 respondents completed 226 questions and an online Self TTO.

In the UK the National Institute for Health and Clinical Excellent (NICE) has mandated the use of a single instrument, the EQ-5D. The argument has been that the use of a single instrument achieves comparability of measurement. The logic of this argument is unambiguously wrong. Analogously we would not achieve comparability in the measurement of medical need through the use of a single and insensitive indicator such as blood pressure. To the contrary, the use of a single insensitive instrument ensures discrimination. EQ-5D primarily measures pain and physical function. Its use for psychological interventions discriminates against these interventions.

Yes. This is one of the strengths of a simple generic instrument. It may be applied weekly, monthly or at any appropriate time interval.

The minimum clinical difference is the clinical or quantitative change in a measure that would typically cause a clinician to change his or her treatment. For a researcher seeking to change practice a sample size is calculated to enable this difference to be detected with a given statistical power (usually 80 percent) at a conventional level of statistical significance (usually 5 percent).

No exact analogy exists in cost utility analysis as clinicians use clinical, not QoL, indices. For policy makers concerned with cost per QALY the relevant data relates to the best estimate where confidence (for each component of the cost per QALY) increases with the sample size.

Nevertheless there may be a context where a researcher wishes to ensure that a change will improve QoL sufficiently that it will be detected by patients. Drummond (1991) suggests a figure of 0.03 for this purpose. Subsequent research has reported that patients detect a change in their health status when the SF-6D changes by 0.04 or the EQ-5D by 0.075 (Walters and Brazier 2005).

However it is important to reiterate that these higher figures should not be confused with minimum changes which are meaningful for QALY calculations. A change of 0.075 has the same impact as a 7.5 percent change in the length or quantity of life.

References:

Drummond M. (1991). ‘Introducing economic and quality of life measures into clinical studies’, Annals of Medicine, Special Edition 33:5, p344-349.

Walters S, Brazier J. (2005). ‘Comparison of the minimally important difference for two health states: EQ-5D and SF-6D’, Quality of Life Research, 14:1523-32.

No. The AQoL assists in the measurement of benefits which are then compared with costs in order to make a decision.

QALYs are designed to measure the average utility of a group of patients or program participants.

See Richardson, McKie, Bariola, (2011) Review and Critique of related multi attribute utility instruments, Research Paper 64, CHE, Monash University (forthcoming in AJ Culyer (ed) Online Encyclopedia of Health Economics, Elsevier Science, San Diego).  This paper describes the construction, similarities and dissimilarities between the major instruments.

Also see Richardson, Iezzi, Khan, Maxwell, (2012) A cross-national comparison of 12 quality of life instruments, MIC Paper 2: Australia, Research Paper 78, CHE Monash University. This paper presents results from a comparison of the major instruments using data from 7720 respondents in five countries. A pairwise comparison of instruments is undertaken which quantifies the advantage of each instrument with respect to different dimensions of the quality of life

In principle the AQoL is similar to other MAU instruments; they all purport to measure the strength of preference for different health states on a 0-1 scale. In practice each of the existing MAU instruments differs in important respects.

Some conceptualise health in terms of disease characteristics: impairment and disability (HUI-I, II and III; 15D; DALY). Others have a heavier emphasis upon handicap: illness induced, or lack of capacity to carry out normal social activities (the AQoL, WHOQoL; SF36 and EuroQoL).

Even when broadly conceptualised in the same way, the descriptive systems of different generic instruments vary considerably with respect to the detail with which they describe different health dimensions. Instruments also differ with respect to the scaling (utility scoring) system adopted.

Some are based upon the use of rating scales (15D and QWB); others have used the time-trade-off (the AQoL, EuroQoL and HUI instruments); one has used the person trade-off (the DALY); and one has used magnitude estimation (Rosser-Kind).