Network meta-analyses could be improved by searching more sources and by involving a librarian.
OBJECTIVE
Network meta-analyses (NMAs) aim to rank the benefits (or harms) of interventions, based on all available randomized controlled trials. Thus, the identification of relevant data is critical. We assessed the conduct of the literature searches in NMAs.


METHODS
Published NMAs were retrieved by searching electronic bibliographic databases and other sources. Two independent reviewers selected studies and five trained reviewers abstracted data regarding literature searches, in duplicate. Search method details were examined using descriptive statistics.


RESULTS
Two hundred forty-nine NMAs were included. Eight used previous systematic reviews to identify primary studies without further searching, and five did not report any literature searches. In the 236 studies that used electronic databases to identify primary studies, the median number of databases was 3 (interquartile range: 3-5). MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials were the most commonly used databases. The most common supplemental search methods included reference lists of included studies (48%), reference lists of previous systematic reviews (40%), and clinical trial registries (32%). None of these supplemental methods was conducted in more than 50% of the NMAs.


CONCLUSIONS
Literature searches in NMAs could be improved by searching more sources, and by involving a librarian or information specialist.
The First Clinical College of Lanzhou University, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China; Evidence-Based Medicine Center, School of Basic Medical Sciences, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China; Clinical Epidemiology Program, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada; Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
Lun
L
Li
Evidence-Based Medicine Center, School of Basic Medical Sciences, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China.
Jinhui
J
Tian
The First Clinical College of Lanzhou University, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China; Evidence-Based Medicine Center, School of Basic Medical Sciences, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China.
Hongliang
H
Tian
Clinical Epidemiology Program, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada; Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
David
D
Moher
The First Clinical College of Lanzhou University, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China.
Fuxiang
F
Liang
The First Clinical College of Lanzhou University, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China.
Tongxiao
T
Jiang
The First Clinical College of Lanzhou University, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China.
Liang
L
Yao
The First Clinical College of Lanzhou University, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China; Evidence-Based Medicine Center, School of Basic Medical Sciences, No. 199 Donggang West Road, Lanzhou, Gansu 730000, China. Electronic address: kehuyangebm2006@126.com.
Kehu
K
Yang
D016206:Databases, Bibliographic; D006801:Humans; D007255:Information Services; D016247:Information Storage and Retrieval / Q000379:methods*; D016245:Librarians; D016239:MEDLINE; D015201:Meta-Analysis as Topic
Databases searching; Gray literature; Handing searching; Literature search; Network meta-analyses; Search strategy