Division of Support, Systems and Outcomes, Toronto General Hospital, 200 Elizabeth Street, Toronto, ON M5G 2C4, Canada.
BMC Med Res Methodol. 2013 Apr 24;13:59. doi: 10.1186/1471-2288-13-59.
The study describes the methodological challenges encountered in an observational study estimating the effectiveness of colonoscopy in reducing colorectal cancer (CRC) incidence and mortality.
Using Ontario provincial administrative data, we conducted a population-based retrospective cohort study to assess CRC incidence and mortality in a group of average-risk subjects aged 50-74 years who underwent colonoscopy between 1996-2000. We created two study cohorts; unselected and restricted. The unselected cohort consists of subjects aged 50-74 years who were eligible for CRC screening and who had the same primary care physician (PCP) during the period 1996-2000 with at least two years of follow-up. PCPs are general practioners/family physicians who are the main source of health care for Ontarians. The restricted cohort was a nested sample of unselected cohort who were alive and free of CRC as on January 1, 2001 and whose PCPs had at least 10 screen-eligible patients with a colonoscopy referral rate of more than 3%. We compared the outcomes in the two study cohorts; unselected vs. restricted. We then estimated the absolute risk reduction associated with colonoscopy in preventing CRC incidence and mortality in the restricted cohort, using traditional regression analysis, propensity score analysis and instrumental variable analysis.
The unselected cohort (N = 1,341,612) showed that colonoscopy was associated with an increase in CRC incidence (1.61% vs. 4.61%) and mortality (0.36% vs. 1.16%), whereas the restricted cohort (N = 1,089,998) showed that colonoscopy was associated with a reduction in CRC incidence (1.36% vs. 0.84%) and mortality (0.23% vs. 0.15%). For CRC incidence, the absolute risk reduction (ARR) associated with colonoscopy use was 0.52% in an unadjusted model, 0.53% in a multivariate logistic regression model, 0.54% in a propensity score-weighted outcome model, 0.56% in propensity score-matched model, and 0.60% using instrumental variable analysis. For CRC mortality, the ARR was 0.08% in the unadjusted model, multivariate logistic regression model and for a propensity score- weighted outcome model, 0.10% using propensity score matched model and 0.17% using the IVA model.
Colonoscopy use reduced the risk of CRC incidence and mortality in the restricted cohort. The study highlights the importance of appropriate selection of study subjects and use of analytic methods for the evaluation of screening methods using observational data.
本研究描述了在一项观察性研究中估计结肠镜检查在降低结直肠癌（CRC）发病率和死亡率方面的有效性时遇到的方法学挑战。
我们使用安大略省省级行政数据，开展了一项基于人群的回顾性队列研究，以评估一组平均风险的 50-74 岁受试者的 CRC 发病率和死亡率，这些受试者在 1996-2000 年间接受了结肠镜检查。我们创建了两个研究队列；非选择性和限制性。非选择性队列由符合 CRC 筛查条件且在 1996-2000 年期间有相同初级保健医生（PCP）的 50-74 岁受试者组成，并且至少有两年的随访。PCP 是全科医生/家庭医生，是安大略省居民的主要医疗保健来源。受限队列是未选择队列的嵌套样本，截至 2001 年 1 月 1 日，他们仍然活着且没有 CRC，并且他们的 PCP 有至少 10 名符合筛选条件的患者，结肠镜检查转诊率超过 3%。我们比较了两个研究队列的结果；未选择队列与受限队列。然后，我们使用传统回归分析、倾向评分分析和工具变量分析，估计了在受限队列中，结肠镜检查在预防 CRC 发病率和死亡率方面的绝对风险降低。
非选择性队列（N=1341612）显示结肠镜检查与 CRC 发病率（1.61%比 4.61%）和死亡率（0.36%比 1.16%）增加有关，而受限队列（N=1089998）显示结肠镜检查与 CRC 发病率（1.36%比 0.84%）和死亡率（0.23%比 0.15%）降低有关。对于 CRC 发病率，未调整模型中与结肠镜检查使用相关的绝对风险降低（ARR）为 0.52%，多变量逻辑回归模型中为 0.53%，倾向评分加权结果模型中为 0.54%，倾向评分匹配模型中为 0.56%，工具变量分析中为 0.60%。对于 CRC 死亡率，未调整模型、多变量逻辑回归模型和倾向评分加权结果模型中的 ARR 为 0.08%，倾向评分匹配模型为 0.10%，工具变量分析模型为 0.17%。
在受限队列中，结肠镜检查降低了 CRC 发病率和死亡率的风险。该研究强调了使用观察性数据评估筛查方法时，适当选择研究对象和使用分析方法的重要性。
