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Table 1 Characteristics of studies not identified by searching CENTRAL (N = 47)

From: Using the Cochrane Central Register of Controlled Trials to identify clinical trial registration is insufficient: a cross-sectional study

Category Subcategory Number (percentage)
Year of registration 2010 2 (4)
2011 2 (4)
2012 4 (9)
2013 3 (6)
2014 6 (13)
2015 8 (17)
2016 7 (15)
2017 9 (19)
2018 3 (6)
2019 3 (6)
Registries ANZCTR 4 (9)
ClinicalTrials.gov 33 (70)
ChiCTR 1 (2)
IRCT 4 (9)
ISRCTN 2 (4)
JPRN 1 (2)
NTR 1 (2)
ReBEC 1 (2)
Observational studies a Yes 10 (21)
No 37 (79)
Indexed in CENTRAL Yes 31 (66)
No 16 (34)
Included in Cochrane reviews that searched trial registries other than ClinicalTrials.gov or ICTRP Yes 6 (13)
No 41 (87)
Included in Cochrane reviews which types of intervention were Pharmacological 12 (26)
Non-pharmacological 33 (70)
Both 2 (4)
  1. Abbreviations: CENTRAL Cochrane Central Register of Controlled Trials, ANZCTR Australian New Zealand Clinical Trials Registry, ChiCTR Chinese Clinical Trial Registry, ICTRP International Clinical Trials Registry Platform, IRCT Iranian Registry of Clinical Trials, ISRCTN International Standard Randomized Controlled Trial Number Register, JPRN Japan Primary Registries Network, NTR The Netherlands National Trial Register, ReBEC Brazilian Clinical Trials Registry
  2. a Cochrane reviews whose inclusion criteria were limited to controlled trials were included. However, some of these Cochrane reviews also included observational studies as ongoing or unpublished studies