1  Databases

1.1 Clinical Trials Registries

Before clinical trials are performed, they are registered in in dedicated databases, so-called clinical trials registries (CTR). The purpose of this practice is to combat publication bias (see Section 2.5) and to increase transparency and provide access to the clinical trials.

These records clinical trials registries usually comprise information such as study title, short description, study type, eligibility criteria for participants, interventions, randomization, study status and contact information. (See also Glanville et al. (2014), Knelangen et al. (2018)).

Clinical Trial Registries

Country	Website
AU/NZ	Australian and New Zealand Clinical Trials Registry (ANZCTR)
CH	Swiss National Clinical Trials Portal (SNCTP)
CN	Chinese Clinical Trial Registry (ChiCTR)
DE	German Clinical Trials Register (DRKS)
EU	EU Clinical Trials Register (EUCTR) (only records prior to 31-01-2022)
EU	Clinical Trials Information System (CTIS)
IN	Clinical Trials Registry India (CTRI)
NL	Overview of Medical Research in the Netherlands (OMON)
UK	ISRCTN
US	ClinialTrials.gov
WHO	International Clinical Trials Registry Platform (ICTRP)

A comprehensive list of resources with detailed information about the registers and how to search them is maintained by Julie Glanville and Carol Lefebvre.

1.2 Cochrane Library

The Cochrane Library is the collection of Cochrane’s databases, most importantly the Cochrane Database of Systematic Reviews (CDSR) and the Cochrane Central Register of Controlled Trials (CENTRAL), which contain different types evidence to inform healthcare decision-making.

The Cochrane Library is not entirely freely available. Switzerland has complete access to the Cochrane Library due to a national license (currently until 2024).

1.2.1 Cochrane Database of Systematic Reviews (CDSR)

The Cochrane Database of Systematic Reviews (CDSR) is a leading journal (ISSN: 1469-493X) and database for systematic reviews in health care. Cochrane Reviews are published in CDSR, which is accessible via the Cochrane Library.

1.3 PubMed

PubMed is a public and freely available database, maintained by the National Center of Biotechnology Information (NCBI) at the U.S. National Library of Medicine (NLM). In 2024, it contains over 37 million records of biomedical and life science literature.

PubMed and MEDLINE are often used synonymously. However, there is a difference, explained in detail at https://nlm.nih.gov/bsd/difference.html.

PubMed facilitates searching within the databases MEDLINE, PubMed Central (PMC) and Bookshelf.

All records in PubMed possess a unique identifier, the PubMed ID.

Roughly 84 percent of the records in PubMed are indexed using Medical Subject Headings (MeSH).

1.4 PubMed Central

PubMed Central (PMC) is a free full-text database of the NLM. It features Open Access articles from biomedicine and life sciences.

PMC can be searched directly or as part of the PubMed database.

PMC records possess the PubMed Central ID as a digital identifier.

1.5 Embase

Embase (acronym for Excerpta Medica Database) is a subscription-based bibliographic database, produced by Elsevier. In the year 2024 it contains over 32 million references to biomedical and pharmacological articles and conference abstracts.

1.6 Entrez

Entrez ist a cross-database search system maintained by the National Center for Biotechnology Information (NCBI). It comprises 39 databases, such as PubMed, MeSH, the NCBI-Bookshelf and PubMed Central.

Entrez can be accessed using the NCBI website or using the Entrez Programming Utitilites (E-utilities).

Glanville, Julie M., Steven Duffy, Rachael McCool, and Danielle Varley. 2014. “Searching ClinicalTrials.gov and the International Clinical Trials Registry Platform to inform systematic reviews: what are the optimal search approaches?” J Med Libr Assoc 102 (25031558): 177–83. https://doi.org/10.3163/1536-5050.102.3.007.

Knelangen, Marco, Elke Hausner, Maria-Inti Metzendorf, Sibylle Sturtz, and Siw Waffenschmidt. 2018. “Trial Registry Searches for Randomized Controlled Trials of New Drugs Required Registry-Specific Adaptation to Achieve Adequate Sensitivity.” J Clin Epidemiol 94: 69–75. https://doi.org/10.1016/j.jclinepi.2017.11.003.