Marshall R J, Wouters S, Jackson R T
Department of Community Health, University of Auckland, New Zealand.
J Epidemiol Biostat. 2000;5(6):367-73.
Case-crossover studies can be used to assess the effects of transient exposures in acute events by comparing cases' exposures at the time of the event against their usual exposure. Cases from a case-control study can also be analysed by this method if appropriate information is obtained.
We apply the case-crossover method to data collected in a case-control study of acute coronary events, to estimate the risk of alcohol consumption in the 24 h before a coronary event. Two questions, concerning the usual frequency of consuming alcohol and how much was consumed, were used in the analysis. The sensitivity of effect estimates to the two questions and to different ways of eliciting probabilities from them, are examined. The cases and controls were both analysed in the same way, assigning controls a 'pseudo-event' time at random. It is suggested that controls may provide a benchmark to establish whether bias exists in the case-series analysis.
We find that the case-crossover analysis is sensitive to how exposure probabilities are assigned. Adopting a Poisson model for exposures leads to inflated risk estimates. The bias is removed if the control series is used to adjust estimates. There appears to be a small protective effect from alcohol consumption.
Case-crossover designs have considerable potential, but reliable information on usual exposure limits their applicability. More research is required on how best to elicit exposure probabilities.
病例交叉研究可通过比较病例在事件发生时的暴露情况与其通常的暴露情况，来评估急性事件中短暂暴露的影响。如果获得了适当的信息，病例对照研究中的病例也可采用这种方法进行分析。
我们将病例交叉方法应用于急性冠脉事件病例对照研究收集的数据，以估计冠脉事件发生前24小时内饮酒的风险。分析中使用了两个问题，一个关于饮酒的通常频率，另一个关于饮酒量。研究了效应估计值对这两个问题以及从它们得出概率的不同方式的敏感性。病例和对照均采用相同的方式进行分析，随机为对照分配一个“假事件”时间。有人认为对照可作为一个基准，以确定病例系列分析中是否存在偏倚。
我们发现病例交叉分析对暴露概率的分配方式很敏感。采用泊松模型进行暴露分析会导致风险估计值虚高。如果使用对照系列来调整估计值，则可消除偏差。饮酒似乎有轻微的保护作用。
病例交叉设计有很大潜力，但关于通常暴露的可靠信息限制了其适用性。需要更多研究来探讨如何最好地得出暴露概率。
