برآورد مقدار EQ-5D برای مالزی با استفاده از زمان تجارت کردن و روش مقیاس بصری

Objectives To estimate a EQ-5D value set for Malaysia by using time trade-off (TTO) and visual analogue scale (VAS) valuation methods. Methods TTO and VAS valuations were obtained from face-to-face surveys of a convenience sample of patients, caregivers, and health professionals conducted at nine government hospitals in 2004 and 2005. Forty-five EQ-5D questionnaire health states were valued, divided into five sets of 15 health states. Analysis was conducted by using linear additive regression models applying N3 and D1 specifications. Model selection was based on criteria of coefficient properties, statistical significance, and goodness of fit. Results One hundred fifty-two respondents were interviewed, yielding 2174 TTO and 2265 VAS valuations. Respondents found TTO valuations to be more difficult than VAS valuations, and there were more inconsistencies in TTO valuations. All the independent variables in the models were statistically significant and consistent with expected signs and magnitude, except for the D1 specification modeled on TTO valuations. The N3 model provided the best fit for the VAS valuation data, with a mean absolute error of 0.032. Conclusion This study provides a Malaysian EQ-5D questionnaire value set that can be used for cost-utility studies despite survey limitations.

Quality-adjusted life-years are a widely accepted measure of utility used in health economic evaluation studies [1] and [2]. The EuroQol EQ-5D questionnaire, a general measure of health status developed by the EuroQol group [3], is a frequently used instrument that allows the measurement of quality-adjusted life-years. Using the EQ-5D questionnaire, the first population-based health preference value set was developed for the United Kingdom in 1997 [4]. Although the UK value set has been widely used in cost-utility studies, studies have shown that valuation can be systematically different between populations, possibly due to fundamental differences in culture [5], [6] and [7]. This divergence in health preferences between countries has led to recommendations that call for national value sets to be developed for conducting cost-utility analysis [8]. Malaysia is a middle-income developing Southeast Asian country. Because of its multiracial population with a Muslim majority, it is culturally different from the other Asian countries where national EQ-5D value sets have been developed so far. It is debatable whether the value sets currently available can adequately reflect the health preferences of Malaysians in particular or Southeast Asians in general. Therefore, our study sought to develop a value set for EQ-5D health states by using preferences elicited from time trade-off (TTO) and visual analogue scale (VAS) methods from a convenience sample of the Malaysian population.

In this analysis, models derived from VAS valuations were superior to models developed from TTO valuations in terms of coefficient properties, statistical significance, and goodness of fit. Although the N3 and D1 models using VAS valuations were virtually identical, the N3 model was marginally the better model because it had fewer large AEs (AEs > 0.1) between the predicted and actual health state values. Furthermore, the N3 VAS valuation model minimizes the gap between health state 11111 and the next best health state [13], as shown in Table 5 and Appendix 5 in Supplemental Materials found at doi:10.1016/j.jval.2011.11.024. Therefore, value sets derived from the VAS valuation would appear to perform better in the Malaysian setting. This is reinforced by the much lower rate of respondents reporting difficulty with the VAS valuation task (Table 2) and the lower rate of inconsistent valuations when the same respondents valued health states by VAS compared with TTO (Table 3). As can be expected, this Malaysian value set is different from the value sets developed in other countries, such as the original Measure and Valuation in Health study from UK as well as value sets from other Asian countries [4], [5] and [14], as shown in Figure 1.The selection of a VAS-based value set goes against the current preference for TTO-based valuations in Asia. Of the four value sets attempted so far in the Asian region, only the New Zealand valuation from 2003 was derived from the VAS valuation while the two most recent valuations from South Korea from 2008 and 2009 were based on TTO valuations [14], [15] and [16]. EuroQol, however, has stated that “the theoretical and empirical case for favoring one method of health state valuation over another is far from clear cut … for users the choice is between TTO and VAS. [17]” Notwithstanding the current preference for TTO valuations, there are some arguments against the use of TTO valuations. Arnesen and Norhiem [18] argued that assumptions underlying TTO valuations are by no means certain. The authors questioned whether 1) TTO measures the willingness to trade time for improved health; 2) TTO reveals true preferences; 3) life years are a suitable currency; and 4) quality of life is quantifiable. From our own observations of Malaysian respondents, we encountered resistance from some respondents who felt that the hypothetical concept of trading away life years for improved health was culturally unacceptable. Given the relatively strong religiosity of many Malaysians, it would not be surprising for TTO-type valuations to encounter more resistance from respondents compared with the morally more neutral valuation on a VAS scale. The other alternative valuation method is the standard gamble (SG). SG was not used in the current study because TTO valuations are more widely adopted for EQ-5D questionnaire valuation studies [4], [5], [6], [11], [14] and [15]. A recent study indicates that SG might be preferred to TTO for health preference elicitation in neighboring Singapore [19]. Despite some similarities, however, there are important differences in the demographic composition of Malaysia and Singapore that can affect the acceptability of SG questions. Unlike Singapore, Malaysia has a Muslim majority population who tend to consider gambling to be sinful. Therefore, this might influence the suitability of SG as a choice method for Malaysia. Another concern with the study is that it obtained valuations from a respondent population by convenience sampling at dialysis centers whereas EQ-5D questionnaire valuation studies have followed the prescription of the US Public Health Service that the “reference case” preferences are those from a representative sample of the general population with the justification that as the ultimate payers of health care (whether through contributions to health insurance schemes or as taxpayers who fund health systems) the general public's preferences are the ones that count [1] and [20]. There have been arguments that patients may provide higher health state valuations because of strategic biases and that especially in the case of chronic conditions, patients' coping mechanisms may allow them to adapt to living with ill health [20] and [21]. Empirically, the difference between population and patient valuations is less clear, with some studies showing that patients tend to value poor health states significantly higher than the general public while other studies have not detected such systematic differences [20], [22] and [23]. Despite the preference for population-based valuations, it is not absolutely clear that population preferences are superior to patient-based preferences. Choices on whether population or patient perspectives should count are ultimately questions of political theory and ethics. Recent research in the area suggests that from an ethical perspective, there is good justification for preferring a patient perspective than a population-based one [21]. A particular weakness of this value set is that it is derived from a small, nonrandom sample of respondents. Even compared with the smallest sample sizes used to develop EQ-5D questionnaire value sets elsewhere (300 in Spain, 309 in Netherlands [24]), the sample size of 153 in the current study is very small by comparison. This, in part, was unavoidable because of the resource constraints at the time of data collection. Nevertheless, the small sample was collected through face-to-face interviews by only three trained interviewers, which should reduce the variability inherent in large population surveys. In spite of the small sample size, the value sets presented here are statistically valid and highly significant. In conclusion, despite the limitations of the current study, until such time as a larger valuation is conducted either in Malaysia or in another country with closer cultural similarities to Malaysia, the value set presented here should be considered for use in cost-utility studies in Malaysia and other Southeast Asian countries.