The type of bias mainly includes publica-tion bias,literature retrieval bia s and literature inclusion bias,amo ng which the publication bias is the hardest o vercome.

• 偏倚的类型主要包括文献发表性偏倚、文献查寻偏倚和文献筛选偏倚,其中最难克服的是文献发表性偏倚。