Preference-based measures to obtain health state utility values for use in economic evaluations with child-based populations: a review and UK-based focus group assessment of patient and parent choices.

BACKGROUND: No current guidance is available in the UK on the choice of preference-based measure (PBM) that should be used in obtaining health-related quality of life from children. The aim of this study is to review the current usage of PBMs for obtaining health state utility values in child and adolescent populations, and to obtain information on patient and parent-proxy respondent preferences in completing PBMs in the UK. METHODS: A literature review was conducted to determine which instrument is most frequently used for child-based economic evaluations and whether child or proxy responses are used. Instruments were compared on dimensions, severity levels, elicitation and valuation methods, availability of value sets and validation studies, and the range of utility values generated. Additionally, a series of focus groups of parents and young people (11-20 years) were convened to determine patient and proxy preferences. RESULTS: Five PBMs suitable for child populations were identified, although only the Health Utilities Index 2 (HUI2) and Child Heath Utility 9D (CHU-9D) have UK value sets. 45 papers used PBMs in this population, but many used non-child-specific PBMs. Most respondents were parent proxies, even in adolescent populations. Reported missing data ranged from 0.5 to 49.3%. The focus groups reported their experiences with the EQ-5D-Y and CHU-9D. Both the young persons' group and parent/proxy groups felt that the CHU-9D was more comprehensive but may be harder for a proxy to complete. Some younger children had difficulty understanding the CHU-9D questions, but the young persons' group nonetheless preferred responding directly. CONCLUSION: The use of PBMs in child populations is increasing, but many studies use PBMs that do not have appropriate value sets. Parent proxies are the most common respondents, but the focus group responses suggest it would be preferred, and may be more informative, for older children to self-report or for child-parent dyads to respond.

Willingness-to-pay and demand curves: a comparison of results obtained using different elicitation formats.

Health economists use "willingness-to-pay" to assess the prospective value of novel interventions. The technique remains controversial, not least with respect to the formats under which values are elicited. The paper analyses the results of a series of studies of the same intervention valued by the same population, in which different elicitation formats were employed. The findings support the hypothesis that data collected using different formats give rise to different demand curves, from which different inferences about demand elasticity, profitability and consumer surplus will be derived. Judgements as to the relative merits of rival interventions depend crucially upon whichever format has been used to evaluate each intervention.

Comparing willingness-to-pay: bidding game format versus open-ended and payment scale formats.

The willingness-to-pay technique is being used increasingly in the economic evaluation of new health care technologies. Clinical trials of two methods of screening for colorectal cancer are currently being conducted in the UK and willingness-to-pay for screening has already been estimated by means of a questionnaire survey, using open-ended (OE) and payment scale (PS) formats. This paper addresses the same medical issue, although it elicits willingness-to-pay values by means of a bidding game in an interview setting. Interviews were conducted with 106 subjects in Nottingham. The bidding game format produced considerably higher valuations than had either of the previous questionnaire formats, whilst the significant differences between agreed valuations obtained using different initial bids supported the existence of starting-point bias in the bidding game. As with the questionnaire study, the majority of interview subjects offered relative valuations of tests at variance with their expressed preferences over the same tests. Given the significant difference in valuations generated by different formats, it follows that the economic case for preferring any one technology over others will depend considerably upon whichever format happens to have been used to generate the valuations.

Evidence of range bias in contingent valuation payment scales.

The payment scale format has been widely used in willingness-to-pay studies in health care. Concerns have been expressed that the format is, in theory, prone to range bias, although this proposition has not been tested directly. We report the findings of a contingent valuation questionnaire study of colorectal cancer screening, wherein different subjects were provided with payment scales of two different lengths. Whilst the long-scale instrument included scale values up to pound 1000, the short-scale version extended only to pound 100. After controlling for inter-sample differences in, for example, income, education and health behaviour, it emerged that the long-scale instrument produced a mean willingness to pay more than 30% higher than that resulting from the short-scale version. We believe our findings to be strongly supportive of the likelihood of range bias in payment-scale instruments, with important consequences for the estimation of both average valuation and consumer surplus.

A comparison of two methods for eliciting contingent valuations of colorectal cancer screening.

Willingness-to-pay (WTP) is being used increasingly in health technology assessment, although a number of methodological issues remain unresolved. Using data obtained from a randomised questionnaire survey, we investigated the metrical properties of two WTP formats, the open-ended question versus the payment scale, in the context of screening for colorectal cancer. Approximately, 2800 responses were analysed. Household income, attitudes toward health promotion and personal risk perceptions were the principal determinants of the nature and value of response. In comparison with the open-ended format, the payment scale achieved a higher completion rate and generated higher valuations. We believe that a framing effect is the most plausible explanation for these differences in performance. In contrast to previous findings, we do not find subjects' perceptions of the resource cost of interventions to be a convincing explanation for either their WTP values or inconsistencies between values and preferences. Although a proportion of respondents protested at the notion of valuation, the majority offer positive valuations, although typically of a lower value that non-protesters.

Eliciting willingness to pay: comparing closed-ended with open-ended and payment scale formats.

Willingness to pay (WTP) is increasingly being used as a measure of valuation in health technology assessment. A variety of formats for eliciting values are available, although the relative virtues of each remain the subject of methodological controversy. This article compares valuation results obtained using a WTP survey instrument in a closed-ended format with those obtained from instruments using open-ended and payment scale formats. Samples of subjects were drawn from a general population, and all were asked to value the same intervention--alternative methods of screening for colorectal cancer. It was discovered that, whereas the open-ended and payment scale formats produced broadly similar valuations, the closed-ended format produced significantly higher WTP valuations and different justifications for those valuations. It is hypothesized that anchoring and yea-saying effects explain these differences and that the closed-ended format triggers a different response mode in subjects.