Table 2 Inclusion and exclusion criteria

KQ 1: Methods to recover falsely excluded studies

• Reference list checking of included studies

• Similarity searches (i.e., related articles)

• Forward citation tracking of included studies using citation indexes

• Google Scholar search

• Contacting experts/researchers/companies/other stakeholders

Other methods

KQ 2: Potential predictors of false exclusion

• Study design

• Main objective

• Sample size

• Country of conduct

• Year of publication

• Structure and content of abstract (e.g., only title available, no abstract, uninformative abstract)

• Language of publication

• Risk of bias

• Database indexing of studies (e.g., PubMed listing)

• Publication type

• Journal in which the study is published

• Impact factor of journal in which the study is published

• Others

Outcomes

• Proportion of falsely excluded studies that could be recovered (KQ 1)

• Recall, precision, numbers needed to read (NNR) of supplementary searches (KQ 1)

• Impact of recovered studies on meta-analysis results and conclusions (KQ 1)

• Falsely excluded studies by characteristics (KQ 2)

• Falsely excluded studies by predictors (KQ 2)

Other outcomes

Study design

• Systematic reviews (KQ 1, 2)

• Randomized/nonrandomized trials (KQ 1, 2)

• Prospective and retrospective, controlled and uncontrolled observational studies (KQ 1, 2)

Nonempirical publications (e.g., editorials, letters)

Date of search

Published 1999 or later

1998 and earlier

Publication language

No restrictions

No restrictions