iBMG/iMTA, Erasmus University Rotterdam, PO Box 1738, 3000 DR Rotterdam, The Netherlands.
Qual Life Res. 2012 Feb;21(1):25-34. doi: 10.1007/s11136-011-9917-4. Epub 2011 Apr 21.
An important assumption underlying the quality-adjusted life year (QALY) model is that people trade off life years against health in the same proportion irrespective of the number of remaining life years. This is known as the constant proportional trade-offs (CPTO) condition. Previous studies have produced mixed empirical evidence about the validity of CPTO. This paper is the first to test CPTO using the time trade-off (TTO) method for a broad time horizon.
In a sample of 83 students, we use a choice based TTO protocol to elicit TTO scores for back pain, using ten different gauge durations ranging between 1 and 46 years. The TTO scores are corrected for discounting, which is elicited by means of the direct method.
We find average TTO scores varying between 0.72 and 0.81. Although the scores do not differ much for different durations in absolute terms, some differences are significant, rejecting CPTO, with and without correcting for discounting. No clear relationship between TTO scores and gauge duration is found. An anchoring and rounding heuristic to some extent explains our results.
Our findings highlight the importance of elicitation methods and context dependencies in QALY measurement and warrant detailed investigation of their influence.
质量调整生命年（QALY）模型的一个重要假设是，无论剩余生命年限如何，人们都会以相同的比例权衡生命年和健康。这被称为恒定比例权衡（CPTO）条件。先前的研究对 CPTO 的有效性产生了混合的经验证据。本文首次使用广泛的时间范围的时间权衡（TTO）方法来测试 CPTO。
在 83 名学生的样本中，我们使用基于选择的 TTO 协议来引出背痛的 TTO 分数，使用十种不同的量表持续时间在 1 到 46 年之间。TTO 分数经过贴现校正，通过直接法引出。
我们发现平均 TTO 分数在 0.72 到 0.81 之间变化。尽管在绝对值上不同持续时间的分数差异不大，但一些差异具有统计学意义，拒绝了 CPTO，无论是校正还是未校正贴现。没有发现 TTO 分数和量表持续时间之间有明显的关系。一种锚定和舍入启发式在一定程度上解释了我们的结果。
我们的发现强调了在 QALY 测量中，启发式和语境依赖的重要性，需要对其影响进行详细调查。
