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

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

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)
Observational studies ^a	No	37 (79)
Indexed in CENTRAL	Yes	31 (66)
Indexed in CENTRAL	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)

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
^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 However, some of these Cochrane reviews also included observational studies as ongoing or unpublished studies

ISSN: 1471-2288