Skjoldborg Ulla Slothuus, Lauridsen Jørgen, Junker Peter
Institute of Public Health, University of Southern Denmark, Odense, Denmark.
Value Health. 2009 Jan-Feb;12(1):153-8. doi: 10.1111/j.1524-4733.2008.00402.x.
To investigate the issue of conjoint reliability over time.
A discrete choice experiment was applied using scenarios that describe the effect of treating rheumatoid arthritis patients with TNF-alpha inhibitors, a novel class of highly effective, but expensive antirheumatic agents. Respondents participated in three face-to-face interviews over a period of 4 months. Reliability was measured both at the input level, where the consistency of matches made by respondents to the Discrete Choice Experiment (DCE) question between replications was determined, and at the output level, where the parameters of the conjoint model were estimated and tested for joint significance and willingness to pay (WTP) confidence intervals were calculated.
Input level: Of the 1661 choices made in survey 1, 1316 were repeated in survey 2. Based on the observed number of consistently repeated choices and the expected number by chance, a fair agreement between the choices in the two surveys (chi2 = 324) was found. Of the 998 consistently repeated choices from survey 1 to survey 2, 818 were repeated in survey 3. There was again a high level of consistency between the choices in surveys 1 and 2 and the final choice in survey 3. Output level: The confidence intervals for WTP figures in surveys 1 and 2 and 1 and 3 were overlapping, implying that the DCE was reliable at the output level over time.
The proportion of consistent responses was higher than would be expected by chance. Conjoint reliability over time was found both at the input and output level.
研究联合可靠性随时间变化的问题。
采用离散选择实验，使用描述用肿瘤坏死因子-α抑制剂治疗类风湿关节炎患者效果的情景，肿瘤坏死因子-α抑制剂是一类新型的高效但昂贵的抗风湿药物。受访者在4个月的时间内参加了三次面对面访谈。在输入层面测量可靠性，即确定受访者在重复实验中对离散选择实验（DCE）问题做出的匹配的一致性；在输出层面测量可靠性，即估计联合模型的参数并测试其联合显著性，计算支付意愿（WTP）置信区间。
输入层面：在调查1中做出的1661个选择中，1316个在调查2中重复出现。根据观察到的一致重复选择的数量和随机预期数量，发现两次调查中的选择之间有合理的一致性（卡方=324）。在从调查1到调查2的998个一致重复选择中，818个在调查3中重复出现。调查1和2中的选择与调查3中的最终选择之间再次存在高度一致性。输出层面：调查1和2以及调查1和3中WTP数值的置信区间相互重叠，这意味着随着时间推移，DCE在输出层面是可靠的。
一致反应的比例高于随机预期。在输入和输出层面均发现联合可靠性随时间变化。
