HERC: Measuring Health Preference
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Measuring Health Preference

This page provides a brief overview of measuring Quality-Adjusted Life Years (QALYs) and the VR-36/VR-12. For more complete information on preference measurement, see the HERC Guidebook: Preference Measurement in Economic Analysis (2007).

Measuring Quality-Adjusted Life Years

To compare the value of one treatment with another, you need an outcome measure that works across different health states. This rules out disease-specific quality of life measures as they only reflect a specific disease or illness.

In addition, the outcome measure must also work as a measure of preference. Preference measures not only measure health status, but they also measure how the individual values the current health state. The valuation of the current health state usually covers the spectrum from full health to death.

To date, the quality adjusted life year (QALY) model is the preferred metric for estimating the health effects (Gold et al., 1996). QALYs are estimated by multiplying each life year gained with an intervention by a quality-weighting factor that reflects the individual's quality of life in the health state for that year. Utilities, measured on a scale from zero (death or the worst health imaginable) to one (perfect health), can be used as quality-weighting factors. See Gold et al., 1996 for details.

There are different ways to find quality weights. The easiest is to use published reports and league tables. Besides Medline, a great resource for this is the Tufts Cost-Effectiveness Analysis Registry.

If existing utility weights do not meet your needs, you may need to collect weights. In doing so, sampling issues should be considered carefully (see Gold et al., 1996). The estimation of the quality weights for a given period (i) and treatment (k) requires the successful completion of two tasks:

  • Measuring the impact of an intervention on the distribution of health states. This task requires that the health states influenced by the treatment are completely characterized.
  • Assessing the preferences (utilities) for these alternative health states.

This two-step estimation process can be done with different methods.

Indirect utility assessment

Direct utility assessment

  • Rating Scales
  • Standard gamble (SG)
  • Time tradeoff (TTO)

A key distinction between the methods is the how they handle risk. The Standard Gamble makes the respondent consider the risk of death. The Time Tradeoff method asks the person to consider a tradeoff with years of life. Some say that the TTO is cognitively easier to understand than SG, although the jury is still out on this. Usually the SG and TTO methods require interview administration, although a lot work is being done to use computer and Internet administration. Given the logisitical complexities, many people turn to the rating scales. The rating scales, however, do not require people to consider risk. There is a controversy over the importance of including risk (See Gold et al, 1996, p 118).

It is also important to note that these methods usually yield different utility weights. This has led some people to use multiple methods.


VR-36 and VR-12

The "Veterans RAND 36-Item Health Survey" (VR-36 and formerly the Veterans SF-36) was developed from the original RAND version of the 36-Item Health Survey version 1.0 (also known as MOS SF-36) at the RAND Corporation as part of the Medical Outcomes Study. The VR-12 ("Veterans RAND 12-Item Health Survey," formerly the Veterans SF-12) was derived from the VR-36. While the names of these assessment tools have changed, the content of the instruments has not.

There is no cost to use the VR-36 and VR-12. However, so that the developers can monitor the use of these instruments, researchers must obtain permission by requesting to use the instrument in a letter on institutional letterhead to Dr. Lewis Kazis. The letter should state that the requestor agrees to the terms and conditions given by the RAND Corporation and indicate that the user plans to give appropriate acknowledgements for the VR-12 and/or VR-36. An abstract of the project should be included with the request.

Is any one assessment tool better than the others?

VR-36/VR-12 vs. SF-36/SF-12

The VR instruments use five-point response choices for seven items in the VR-36 and four items in the VR-12. Response choices that were originally dichotomous (a two-point yes/no choice) are now five-point response choices: "no, none of the time", "yes, a little of the time", "yes, some of the time", "yes, most of the time" and "yes, all of the time". These answers then contribute to the scales for role limitations due to physical and emotional problems. Expanding these scales in the VR instruments has resulted in a reduction of floor and ceiling effects, with important gains in the scales’ distributional properties and increases in reliability and validity.3 The VR-36 and VR-12 also include two additional items to assess physical and emotional health change, in contrast to the single general change item in the SF-36.

VR12/SF-12 vs. VR36/SF-36

The SF-12 is a shorter alternative to the SF-36 but it reproduces the eight-scale profile with fewer levels than the SF-36 and produces less precise scores. Because confidence intervals for group averages in health scores are largely determined by sample size, these differences are not as important for large group studies. The SF-12 improves efficiency and lowers cost for both profiles and summary scales, and is most appropriate for use in large samples of general and specific populations as well as large longitudinal studies of health outcomes. Selim and colleagues have also developed the VR-6D algorithm which computes health state utilities for the VR-12. Utilities or preference-based scores reflect values on health states and are essential for cost-effectiveness analysis.

For a list of studies in which the VR-36 and VR-12 was used for measuring health-related quality of life, please refer to Iqbal 2009.

There are some limitations in using the assessment tools. Researchers interested in this topic should consult Kazis 2004a, Kazis 2004b, Keller 1999, Rose 2008, Selim 2006, and Wilson 2000.


References

Gold MR, Siegel JE, Russell LB, Weinstein MC. Cost-effectiveness in health and medicine. New York: Oxford University Press; 1996. see p. 285 et. seq.

Gyrd-Hansen D, Sogaard J. Discounting life-years: whither time preference? Health Econ 1998; 7:121-7.

Iqbal, SU, Rogers, W, Selim, A, Qian, S, Lee, A, Ren, XS, Rothendler, JD, Miller, D, Kazis, LE. The veterans RAND 12 item health suvery (VR-12): what it is and how it is used. Center for Health Quality, Outcomes, and Economic Research, A Health Services Research and Development Center of Excellence, VA Medical Center, Bedford, MA, USA.

Kamlet MS. A framework for cost-utility analysis of government healthcare programs: Office of Disease Prevention and Health Promotion, Public Health Service, U.S. Department of Health and Human Services; 1992.

Kazis, L. E., Miller, D. R., Clark, J. A., Skinner, K. M., Lee, A., Ren, X. S., et al. Improving the response choices on the veterans SF-36 health survey role functioning scales: Results from the Veterans Health Study. J Ambul Care Manage. 2004 Jul-Sep;27(3):263-80.

Kazis, L. E., Lee, A., Spiro, A., 3rd, Rogers, W., Ren, X. S., Miller, D. R., et al. (2004). Measurement comparisons of the medical outcomes study and veterans SF-36 health survey. Health Care Financing Review. 2004 Summer;25(4):43-58.

Kazis LE, Selim A, Rogers W, Ren XS, Lee A, Miller DR. Veterans RAND 12-Item Health Survey (VR-12): A White Paper Summary. Unpublished manuscript. http://www.hosonline.org/surveys/hos/download/Veterans_RAND_12_Item_Health_Survey_White_Paper_Summary.pdf.

Keller SD, Ware JE, Jr., Hatoum HT, Kong SX. The SF-36 Arthritis-Specific Health Index (ASHI): II. Tests of validity in four clinical trials. Med Care. 1999 May;37(5 Suppl):MS51-60.

Selim AJ, Berlowitz D, Fincke G, et al. Use of risk-adjusted change in health status to assess the performance of integrated service networks in the Veterans Health Administration. Int J Qual Health Care. 2006 Feb;18(1):43-50.

Selim AJ, Rogers W, Fleishman JA, et al. Updated U.S. population standard for the Veterans RAND 12-item Health Survey (VR-12). Qual Life Res. 2009 Feb;18(1):43-52.

Selim AJ, Rogers W, Qian SX, Brazier J, Kazis LE. A preference-based measure of health: the VR-6D derived from the veterans RAND 12-Item Health Survey. Qual Life Res. 2011 Oct;20(8):1337-47.

The SF-12: An Even Shorter Health Survey: Version 2.0. SF-36.org Web Site. //www.sf-36.org/tools/sf12.shtml.

Torrance, G. W., & Feeny, D. (1989). Utilities and quality-adjusted life years. Int J Technol Assess healthcare, 5(4), 559-75.

Wilson D, Parsons J, Tucker G. The SF-36 summary scales: problems and solutions. Soz Praventivmed. 2000;45(6):239-46.