Pekkanen Juha, Sunyer Jordi, Chinn Susan
Unit of Environmental Epidemiology, National Public Health Institute, P.O. Box 95, 70701 Kuopio, Finland.
J Clin Epidemiol. 2006 Mar;59(3):281-9. doi: 10.1016/j.jclinepi.2005.07.013.
When estimating incidence risk ratios in follow-up studies, subjects testing positive for the disease at baseline are excluded. Although the effect of disease misclassification on estimated incidence risk ratios has otherwise been extensively explored, the effect of disease misclassification at baseline has not previously been analyzed.
The design was theoretical calculations assuming dichotomous disease and a follow-up study with a baseline and a follow-up examination, analyzed using cumulative incidence. Calculations consider nondifferential misclassification of disease mainly at baseline, but no misclassification of exposure.
Nondifferential misclassification of disease at baseline can lead to bias either away or toward null in estimated cumulative incidence risk ratios. This bias is mainly a function of sensitivity at baseline, because imperfect sensitivity leads to failure to exclude all diseased subjects from the follow-up. Imperfect specificity at baseline has less effect. Bias is increased with high true prevalence of disease and low true incidence. Bias is also increased with large differences in true risk ratios at baseline and at follow-up, because observed incidence risk ratios in the presence of misclassification reflect both the true association at baseline and at follow-up.
Nondifferential disease misclassification at baseline examination of a follow-up study can lead to over- or underestimation of the cumulative incidence risk ratios. The bias can be substantial for disease with low incidence and high prevalence, such as asthma or myocardial infarction. The results underscore the need to select a highly sensitive test for disease at baseline to exclude all diseased subjects from the follow-up.
在随访研究中估计发病风险比时，基线时疾病检测呈阳性的受试者会被排除。尽管疾病误分类对估计的发病风险比的影响已得到广泛探讨，但基线时疾病误分类的影响此前尚未进行分析。
设计采用理论计算，假设疾病为二分法，随访研究包括基线检查和随访检查，使用累积发病率进行分析。计算考虑主要在基线时疾病的无差异误分类，但暴露无误分类。
基线时疾病的无差异误分类可导致估计的累积发病风险比出现远离或趋向无效值的偏差。这种偏差主要是基线时灵敏度的函数，因为灵敏度不完善会导致未能将所有患病受试者排除在随访之外。基线时特异性不完善的影响较小。疾病的真实患病率高而真实发病率低时，偏差会增加。基线和随访时真实风险比差异大时，偏差也会增加，因为存在误分类时观察到的发病风险比反映了基线和随访时的真实关联。
随访研究基线检查时疾病的无差异误分类可导致累积发病风险比被高估或低估。对于哮喘或心肌梗死等发病率低但患病率高的疾病，偏差可能很大。结果强调在基线时需要选择对疾病高度敏感的检测方法，以将所有患病受试者排除在随访之外。
