Department of Obstetrics and Gynecology, School of Medicine and Duke Global Health Institute, Duke University, Durham, NC, USA.
Stat Med. 2012 Aug 15;31(18):2000-9. doi: 10.1002/sim.5316. Epub 2012 Apr 11.
The parametric g-formula can be used to contrast the distribution of potential outcomes under arbitrary treatment regimes. Like g-estimation of structural nested models and inverse probability weighting of marginal structural models, the parametric g-formula can appropriately adjust for measured time-varying confounders that are affected by prior treatment. However, there have been few implementations of the parametric g-formula to date. Here, we apply the parametric g-formula to assess the impact of highly active antiretroviral therapy on time to acquired immune deficiency syndrome (AIDS) or death in two US-based human immunodeficiency virus cohorts including 1498 participants. These participants contributed approximately 7300 person-years of follow-up (49% exposed to highly active antiretroviral therapy) during which 382 events occurred and 259 participants were censored because of dropout. Using the parametric g-formula, we estimated that antiretroviral therapy substantially reduces the hazard of AIDS or death (hazard ratio = 0.55; 95% confidence limits [CL]: 0.42, 0.71). This estimate was similar to one previously reported using a marginal structural model, 0.54 (95% CL: 0.38, 0.78). The 6.5-year difference in risk of AIDS or death was 13% (95% CL: 8%, 18%). Results were robust to assumptions about temporal ordering, and extent of history modeled, for time-varying covariates. The parametric g-formula is a viable alternative to inverse probability weighting of marginal structural models and g-estimation of structural nested models for the analysis of complex longitudinal data.
参数 g 公式可用于对比任意治疗方案下潜在结局的分布。与结构嵌套模型的 g 估计和边际结构模型的逆概率加权一样，参数 g 公式可以适当地调整受先前治疗影响的测量时变混杂因素。然而，到目前为止，参数 g 公式的实现还很少。在这里，我们应用参数 g 公式评估高效抗逆转录病毒疗法对两个基于美国的人类免疫缺陷病毒队列中获得性免疫缺陷综合征（AIDS）或死亡的时间的影响，这些队列包括 1498 名参与者。这些参与者提供了大约 7300 人年的随访（49%暴露于高效抗逆转录病毒疗法），在此期间发生了 382 起事件，有 259 名参与者因辍学而被删失。使用参数 g 公式，我们估计抗逆转录病毒疗法显著降低 AIDS 或死亡的风险（危险比=0.55；95%置信区间[CL]：0.42，0.71）。这一估计与使用边际结构模型报告的估计值相似，为 0.54（95% CL：0.38，0.78）。AIDS 或死亡风险的 6.5 年差异为 13%（95% CL：8%，18%）。结果对于时变协变量的时间顺序和建模历史程度的假设是稳健的。参数 g 公式是分析复杂纵向数据的边际结构模型的逆概率加权和结构嵌套模型的 g 估计的可行替代方法。
