Mrus Joseph M, Yi Michael S, Freedberg Kenneth A, Wu Albert W, Zackin Robert, Gorski Heather, Tsevat Joel
Health Services Research and Development, Cincinnati VA Medical Center, Ohio, USA.
Med Decis Making. 2003 Sep-Oct;23(5):414-21. doi: 10.1177/0272989X03256884.
Visual analog scale (VAS) scores are used as global quality-of-life indicators and, unlike true utilities (which assess the desirability of health states v. an external metric), are often collected in HIV-related clinical trials. The purpose of this study was to derive and evaluate transformations relating aggregate VAS scores to utilities for current health in patients with HIV/AIDS.
HIV-specific transformations were developed using linear and nonlinear regression to attain models that best fit mean VAS and standard gamble (SG) utility values directly derived from 299 patients with HIV/AIDS participating in a multicenter study of health values. The authors evaluated the transformations using VAS and SG utility values derived directly from patients in other HIV/AIDS studies. Derived transformations were also compared with published transformations.
A simple linear transformation was derived (u = 0.44v + 0.49), as was the exponent for a curvilinear model (u = 1 - [1 - v]1.6), where u = the sample mean utility and v the sample mean VAS score. The curvilinear transformation predicted values within 0.10 of the actual SG utility in 5 of 8 estimates and within 0.05 in 3 of 8 estimates (absolute error ranged from -0.01 to +0.21). The linear transformation performed somewhat better, predicting within 0.10 of the actual SG value in 6 of 8 cases and within 0.05 in 5 of 8 estimates (absolute error ranged from -0.05 to +0.13). An alternative linear model (u = v + 0.018) derived from the literature performed similarly to our linear model (7 of 8 predictions within 0.10, 1 of 8 estimates within 0.05, and absolute error ranging from -0.15 to +0.10), whereas an alternative published curvilinear model (u = 1 - [1 - v]2.3) performed the least well (2 of 8 estimates within 0.10 of the actual values and no estimates within 0.05).
Predicted utilities are a reasonable alternative for use in HIV/AIDS decision analyses and cost-effectiveness analyses. Linear transformations performed better than curvilinear transformations in this context and can be used to convert aggregate VAS scores to aggregate SG values in large HIV/AIDS studies that collect VAS data but not utilities.
视觉模拟量表（VAS）评分用作整体生活质量指标，与真正的效用值（评估健康状态相对于外部指标的可取性）不同，VAS评分常在HIV相关临床试验中收集。本研究的目的是推导并评估将HIV/AIDS患者当前健康状况的VAS总分转化为效用值的转换方法。
利用线性和非线性回归开发HIV特异性转换方法，以获得最适合直接源自参与一项健康价值观多中心研究的299例HIV/AIDS患者的平均VAS和标准博弈（SG）效用值的模型。作者使用直接源自其他HIV/AIDS研究患者的VAS和SG效用值评估这些转换方法。还将推导的转换方法与已发表的转换方法进行比较。
得出一个简单的线性转换方法（u = 0.44v + 0.49），以及一个曲线模型的指数（u = 1 - [1 - v]1.6），其中u为样本平均效用值，v为样本平均VAS评分。曲线转换方法在8次估计中有5次预测值与实际SG效用值相差在0.10以内，8次估计中有3次相差在0.05以内（绝对误差范围为-0.01至+0.21）。线性转换方法表现稍好，8例中有6例预测值与实际SG值相差在0.10以内，8次估计中有5次相差在0.05以内（绝对误差范围为-0.05至+0.13）。从文献中得出的另一种线性模型（u = v + 0.018）的表现与我们的线性模型相似（8次预测中有7次相差在0.10以内，8次估计中有1次相差在0.05以内，绝对误差范围为-0.15至+0.10），而另一种已发表的曲线模型（u = 1 - [1 - v]2.3）表现最差（8次估计中有2次与实际值相差在0.10以内，没有估计相差在0.05以内）。
预测效用值是用于HIV/AIDS决策分析和成本效益分析的合理替代方法。在此背景下，线性转换方法比曲线转换方法表现更好，可用于在收集VAS数据但未收集效用值的大型HIV/AIDS研究中将VAS总分转换为SG总值。
