Tarone R E, Kaune W T, Linet M S, Hatch E E, Kleinerman R A, Robison L L, Boice J D, Wacholder S
Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland 20892, USA.
Occup Environ Med. 1998 May;55(5):333-9. doi: 10.1136/oem.55.5.333.
To investigate the reproducibility of wire codes to characterise residential power line configurations and to determine the extent to which wire codes provide a proxy measure of residential magnetic field strength in a case-control study of childhood leukaemia conducted in nine states within the United States.
Misclassification of wire codes was assessed with independent measurements by two technicians for 187 residences. The association between categories of wire code and measured level of magnetic field was evaluated in 858 residences with both a wire code measurement and a 24 hour measurement of the magnetic field in the bedroom. The strength of the association between category of wire code and risk of leukaemia was examined in two regions with different average levels of magnetic field in homes with high categories of wire code.
The reproducibility of any of three different classifications of wire codes was excellent (kappa > or = 0.89). Mean and median magnetic fields, and the percentage of homes with high magnetic fields increased with increasing category for each of the wire code classification schemes. The size of the odds ratios for risk of leukaemia and high categories of wire code did not reflect the mean levels of the magnetic field in those categories in two study regions.
Misclassification of categories of wire code is not a major source of bias in the study. Wire codes provide a proxy measure of exposure to residential magnetic fields. If magnetic fields were a risk factor for leukaemia, however, there would be some attenuation of risk estimates based on wire codes because of misclassification of exposure to magnetic fields at both extremes of the wire code range. The lack of an association between high categories of wire code and risk of leukaemia cannot be explained by a failure of the wire code classification schemes to estimate exposure to magnetic fields in the study area.
在美国九个州开展的一项儿童白血病病例对照研究中，调查电线编码用于描述住宅电力线配置的可重复性，并确定电线编码在多大程度上可作为住宅磁场强度的替代指标。
由两名技术人员对187处住宅进行独立测量，评估电线编码的错误分类情况。在858处住宅中，同时进行了电线编码测量和卧室磁场24小时测量，评估电线编码类别与测量的磁场水平之间的关联。在电线编码类别较高的住宅中，磁场平均水平不同的两个地区，研究电线编码类别与白血病风险之间关联的强度。
三种不同的电线编码分类方法中的任何一种的可重复性都非常好（kappa≥0.89）。对于每种电线编码分类方案，平均和中位数磁场以及高磁场住宅的百分比都随着类别增加而增加。在两个研究地区，白血病风险的比值比大小和高类别电线编码并未反映这些类别中的磁场平均水平。
电线编码类别的错误分类不是该研究中偏差的主要来源。电线编码可作为住宅磁场暴露的替代指标。然而，如果磁场是白血病的一个风险因素，由于在电线编码范围两端的磁场暴露错误分类，基于电线编码的风险估计会有一些衰减。电线编码高类别与白血病风险之间缺乏关联，不能用电线编码分类方案未能估计研究区域内的磁场暴露来解释。
