Conway David I, McMahon Alex D, Smith Katrina, Taylor John C, McKinney Patricia A
Dental Public Health Unit, University of Glasgow Medical Faculty Dental School, Glasgow, UK.
J Clin Epidemiol. 2008 Nov;61(11):1187-93. doi: 10.1016/j.jclinepi.2007.12.012. Epub 2008 Jul 10.
We aimed to investigate the association between socioeconomic factors and selection and participation biases in a population-based case-control study of head and neck cancer conducted in the city of Glasgow, UK.
General Practices (GP) of the case subjects were the sampling frame from which age and sex-matched controls were randomly selected. Participant and nonparticipant postcodes of cases and controls were linked to the area-based Scottish Index of Multiple Deprivation. Comparisons of study selection and participation were made with the Glasgow study-base population.
Cases were from significantly more deprived areas than controls. Overall, participation was low for both cases (34.9%) and controls (34.7%). Our overall control sample was not similar to the general population of Glasgow having "over selected" from deprived areas. Individuals from more affluent areas were more likely to participate providing a set of interviewed participants reflecting the socioeconomic distribution of Glasgow.
Low participation rates in case-control studies remain a problem and socioeconomic factors strongly affect participation. A control sample selection biased in one direction was offset by participation bias in the opposite direction -- fortuitously providing a representative control sample. Selecting controls from case GP lists needs to be implemented with care with attention paid to obtaining evidence on the underlying socioeconomic characteristics of GP populations, especially for diseases with a skewed socioeconomic distribution.
在英国格拉斯哥市开展的一项基于人群的头颈癌病例对照研究中，我们旨在调查社会经济因素与选择偏倚和参与偏倚之间的关联。
病例组的全科医生诊所（GP）作为抽样框架，从中随机选取年龄和性别匹配的对照组。病例组和对照组参与者与非参与者的邮政编码与基于区域的苏格兰多重贫困指数相关联。将研究选择和参与情况与格拉斯哥研究基础人群进行比较。
病例组所在地区的贫困程度明显高于对照组。总体而言，病例组（34.9%）和对照组（34.7%）的参与率都很低。我们的总体对照样本与格拉斯哥的普通人群不同，存在从贫困地区“过度选择”的情况。来自较富裕地区的个体更有可能参与，从而提供了一组反映格拉斯哥社会经济分布的受访参与者。
病例对照研究中的低参与率仍然是一个问题，社会经济因素强烈影响参与情况。一个方向的对照样本选择偏倚被相反方向的参与偏倚所抵消——幸运地提供了一个具有代表性的对照样本。从病例组的全科医生名单中选择对照组时需要谨慎实施，注意获取关于全科医生人群潜在社会经济特征的证据，特别是对于社会经济分布不均衡的疾病。
