Department of Environmental Health Sciences, School of Public Health, University of Minnesota, Rochester, MN.
Ann Epidemiol. 2013 Nov;23(11):735-41. doi: 10.1016/j.annepidem.2013.07.021. Epub 2013 Aug 27.
Lead-time is inherent in early detection and creates bias in observational studies of screening efficacy, but its potential to bias effect estimates in risk factor studies is not always recognized. We describe a form of this bias that conventional analyses cannot address and develop a model to quantify it.
Surveillance Epidemiology and End Results (SEER) data form the basis for estimates of age-specific preclinical incidence, and log-normal distributions describe the preclinical duration distribution. Simulations assume a joint null hypothesis of no effect of either the risk factor or screening on the preclinical incidence of cancer, and then quantify the bias as the risk-factor odds ratio (OR) from this null study. This bias can be used as a factor to adjust observed OR in the actual study.
For this particular study design, as average preclinical duration increased, the bias in the total-physical activity OR monotonically increased from 1% to 22% above the null, but the smoking OR monotonically decreased from 1% above the null to 5% below the null.
The finding of nontrivial bias in fixed risk-factor effect estimates demonstrates the importance of quantitatively evaluating it in susceptible studies.
在早期检测中存在领先时间，这会导致筛查效果的观察性研究产生偏倚，但人们并不总是认识到它对危险因素研究中效应估计的潜在偏倚。我们描述了一种常规分析无法解决的这种偏倚形式，并开发了一种量化它的模型。
监测流行病学和结局研究（SEER）数据构成了特定年龄组临床前发病率的估计基础，对数正态分布描述了临床前持续时间分布。模拟假设风险因素或筛查对癌症临床前发病率没有影响的联合零假设，然后从这个零研究中量化风险因素比值比（OR）的偏倚。这种偏差可以作为调整实际研究中观察到的 OR 的因素。
对于这种特殊的研究设计，随着平均临床前持续时间的增加，总体力活动 OR 的偏差从零假设的 1%单调增加到 22%，而吸烟 OR 则从零假设的 1%单调下降到 5%。
在固定风险因素效应估计中发现实质性偏倚，证明了在易感研究中定量评估它的重要性。
