Mark D H
American Medical Association, Chicago, USA.
Fam Med. 1997 Feb;29(2):132-6.
The issue of selection bias is often raised in the critical appraisal of medical studies, but it is often poorly defined and misunderstood. This paper, describes three common patterns of use of the term selection bias and their effects on study results. The three ways in which selection bias is used are related to 1) selection of representative subjects, 2) selection of subjects to exposures, and 3) selection of subjects at outcome. Avoidance of bias in the first of these issues, selection of representative subjects, enhances the ability to generalize a study's results. The other two uses of selection bias relate to the internal validity of studies. The selection of subjects to exposures without randomization in observational studies can distort results because of confounding variables. The selection of study subjects at outcome in case-control and cross-sectional studies can distort study findings if selection into the study is distorted according to exposure status. Readers of medical studies should understand the different implications of these uses to improve their critical evaluation of studies. Writers and discussants should be aware of these differences and provide clarifying details when they use the term.
在医学研究的批判性评价中，选择偏倚问题经常被提及，但它往往定义不清且被误解。本文描述了“选择偏倚”这一术语的三种常见用法及其对研究结果的影响。选择偏倚的三种用法分别与以下方面相关：1）代表性研究对象的选择；2）研究对象对暴露因素的选择；3）研究对象在结局方面的选择。在这些问题中的第一个，即代表性研究对象的选择上避免偏倚，可增强研究结果的推广能力。选择偏倚的另外两种用法与研究的内部效度有关。在观察性研究中，非随机地选择研究对象接受暴露因素，可能因混杂变量而扭曲结果。在病例对照研究和横断面研究中，如果根据暴露状态对纳入研究的选择存在扭曲，那么在结局方面选择研究对象可能会扭曲研究结果。医学研究的读者应理解这些用法的不同含义，以改进他们对研究的批判性评价。作者和讨论者应意识到这些差异，并在使用该术语时提供清晰的细节。
