浅谈系统评价的文献偏倚问题

文献偏倚是指由于无法全面地获得相关的临床研究资料，从而影响系统评价结果的真实性。常见的文献偏倚主要包括：1)文献发表偏倚，指某些研究始终不能被发表或被延迟发表；2)文献查寻偏倚，指系统评价过程中。没有全面地获得已发表的相关文献；3)文献筛选偏倚，是由于文献筛选不当，错误地剔除了某些有用的文献。文献偏倚评估的常用方法是以各研究的样本量为横坐标，作用大小为纵坐标，绘制漏斗形图。

Elementary introduction to studies bias of systematic reviews

Literature bias, which can reduce the validity of a systematic review, comes mainly from the fact that all the related studies can not be collected without exception. The following three types of literature bias are most common. 1) Publication bias. The reason is that some studies can not get published, or the publication has been delayed. 2) Literature retrieval bias. This bias is the result that not all published studies are retrieved during the course of systematic review. 3) Literature inclusion bias. While an improper literature selection strategy is adopted, some useful studies are kicked out by error, leading to such bias. A funnel plot (X-axis is sample size, Y-axis effect) is usually useful to assess literature bias in a systematic review.