Polissar L
Am J Epidemiol. 1980 Feb;111(2):175-82. doi: 10.1093/oxfordjournals.aje.a112885.
Cancer rates are often compared between counties or other geographic units as a method of testing for risk from environmental exposures. Migration between geographic areas greatly reduces the sensitivity of this method. Under simplifying assumptions the quantitative effect of migration on risk estimates is shown using migration and cancer incidence data for the United States. For example, 40--50% of the relative excess risk, defined as the relative risk minus one, is not reflected in the estimated risk for most cancers, when rates are compared between exposed and unexposed counties and migration has taken place during a 30-year latent period. More extreme losses of sensitivity also occur. Under the simplifying assumptions, the quantitative effect of migration on risk estimates is shown as a function of cancer site, latent period, and the type of geographic units for which rates are calculated--states, counties, or places. Also discussed are some implications of these findings for geographically-based studies and additional data needs for assessing the effect of migration.
癌症发病率常被用于比较不同县或其他地理区域，以此作为检测环境暴露风险的一种方法。地理区域间的人口迁移极大地降低了这种方法的敏感性。在简化假设条件下，利用美国的人口迁移和癌症发病率数据，展示了迁移对风险估计的定量影响。例如，当在暴露县和未暴露县之间比较发病率，且在30年的潜伏期内发生了人口迁移时，对于大多数癌症而言，定义为相对风险减一的相对超额风险中有40% - 50%未体现在估计风险中。更极端的敏感性损失也会出现。在简化假设条件下，迁移对风险估计的定量影响表现为癌症部位、潜伏期以及计算发病率所依据的地理单元类型（州、县或地区）的函数。还讨论了这些发现对基于地理区域的研究的一些影响，以及评估迁移影响所需的额外数据。
