Finding studies for systematic reviews: a resource list for researchers

Introduction

The following lists suggest some key sources to search to identify studies for inclusion in systematic reviews. The choice of databases will depend upon the topic of the systematic review and the resources that are available to the review project team. The sources suggested here are not exhaustive and additional resources that cover specific topic areas may be available.

Library websites will often provide a list of available databases with a description of their coverage. Database providers such as Dialog (http://www.dialog.com/) and Ovid (http://tinyurl.com/chwhb8oalso produce lists of their products. Relevant databases may also be identified by looking at the methodology section of other related systematic reviews.

Involving a suitably experienced librarian or information specialist in the systematic review process is recommended as librarians are trained to search efficiently and have a wide knowledge of information sources and how to locate information services. They will also be able to help with document acquisition and record management.

Guidance on how to carry out a systematic literature search is available in Systematic Reviews: CRD’s guidance for undertaking reviews in health care (http://www.york.ac.uk/inst/crd/index_guidance.htm). The chapter on core principles describes how to identify studies, manage the references retrieved by the searches, obtaining documents and writing up the search process. Examples of search strategies and search documentation are given. Further chapters include guidance on searching  for studies of diagnostic tests, public health interventions, adverse effects, economic evaluations and qualitative research.

Research in progress

Identifying research in progress can be important at the planning stage of a systematic review to ensure that the proposed review does not duplicate one currently in progress. Once the review is underway it is equally important to identify any relevant primary studies that are in progress so the research team can obtain any preliminary results and learn when the study is to be completed and the full results available.

PROSPERO
An international database of prospectively registered systematic reviews in health and social care. Key features from the review protocol are recorded and maintained as a permanent record in PROSPERO. This will provide a comprehensive listing of systematic reviews registered at inception, and enable comparison of reported review findings with what was planned in the protocol.  PROSPERO is managed by CRD and funded by the UK National Institute for Health Research (NIHR). 
http://www.crd.york.ac.uk/prospero/

The Cochrane Database of Systematic Reviews
CDSR contains protocols of Cochrane reviews that are planned or in progress. The record includes an abstract, the objectives, an outline of the methods to be used, and contact details for the authors. http://www.thecochranelibrary.com/view/0/index.html

Health Technology Assessment (HTA) database
The HTA database includes records for health technology assessments in progress. The records for these include the title of the project and a link to the organisation conducting the research. The HTA database is available free at http://www.crd.york.ac.uk/crdweb/ as well as being available as part of the Cochrane Library.

HSRProj ( Health Services Research Projects in Progress)
This database of current United States projects in health services research is searchable (along with other databases) on the National Library of Medicine (NLM) gateway at: http://www.nlm.nih.gov/hsrproj/

Many of the clinical trial registers include information about trials that are in progress as well as those that have been completed.

Trials Registers

Since many systematic reviews focus on using the results of randomised controlled trials locating these types of studies may be a priority. While searches of bibliographic databases such as MEDLINE and EMBASE will identify RCTs there are also a number of other resources that should also be used.

CENTRAL
The Cochrane Central Register of Controlled Trials (CENTRAL) is a key resource for those preparing and maintaining systematic reviews. CENTRAL includes citations from MEDLINE, EMBASE, as well as other published and unpublished sources
http://www.thecochranelibrary.com/view/0/index.html

ClinicalTrials.gov
US National Institutes of Health collection of clinical studies sponsored by the NIH, other Federal agencies, the pharmaceutical industry, and non-profit organizations in the United States. This database contains records of @131,000 trials.
http://clinicaltrials.gov/

World Health Organization International Clinical Trials Registry Platform
The WHO ICTRP aims to facilitate the prospective registration of the WHO Trial Registration Data Set for all clinical trials.
http://www.who.int/ictrp/en/

metaRegister of Controlled Trials (mRCT)
The metaRegister of Controlled Trials ( mRCT) provides a search interface to a number of trial sources so that a number of registers can be searched simultaneously.  
http://controlled-trials.com/mrct

Centerwatch
Lists recruiting trials with information for patients as well as professionals.
http://www.centerwatch.com/

IFPMA Clinical Trials Portal
Searchable database of comprehensive information on ongoing clinical trials and results of completed trials conducted by the pharmaceutical industry. http://clinicaltrials.ifpma.org/clinicaltrials/no_cache/en/myportal/index.htm

GlaxoSmithKline Clinical Study Register
The Clinical Study Register provides an easily accessible repository of data from GSK-Sponsored Clinical Studies.
http://www.gsk-clinicalstudyregister.com/

UK Clinical Research Network Portfolio database
The NIHR CRN is building a complete picture of the clinical research currently taking place across the UK. Details of studies which meet eligibility criteria are recorded in the database. Covers England, Scotland, Wales and Northern Ireland. 
http://public.ukcrn.org.uk/search/

Major bibliographic databases

For reviews of health care interventions, MEDLINE and EMBASE are the databases most commonly used to identify potential studies although other bibliographic databases may also be useful. The list below highlights frequently used databases and gives brief details of their coverage and scope. Many of the databases included are available via a number of different routes or interfaces.

Applied Social Science Index and Abstracts
ASSIA covers health, social services, psychology, sociology, economics, politics, race relations and education. It currently contains over 375,000 records from over 500 journals published in 16 different countries, including the UK and the USA. 
Further information about ASSIA is available at:
http://www.csa.com/factsheets/assia-set-c.php

BIOSIS Previews 
BIOSIS is a major database covering the life sciences literature. It contains over 18 million citations from more than 5,500 sources. Most of the content is journal articles but meeting and conference reports, books and patents are also included.  It is available via a number of different search interfaces
Further information about BIOSIS is available at:
http://thomsonreuters.com/content/PDF/scientific/BIOSIS_Factsheet.pdf 
The British Nursing Index (BNI) 
BNI is a bibliographic database indexing 240 UK journals and other English language sources. It has covered all aspects of nursing and midwifery since 1985; a thesaurus was added in 2001 and abstracts have been included in database records since 2004.
Further information about BNI is available at:
http://www.bniplus.co.uk/about_bni.html

Cochrane Database of Systematic Reviews 
CDSR is a collection of regularly updated systematic reviews covering health care. It’s available as part of the Cochrane Library. 
Further information about CDSR and the Cochrane Library is available at:
http://www.cochrane.org/.

Cumulative Index to Nursing and Allied Health Literature (CINAHL)
This database covers all aspects of nursing and allied health including occupational therapy, emergency services and social services in health care. The records include a range of publication types in addition to journal articles.
Further information about CINAHL is available at:
http://www.ebscohost.com/cinahl/

Database of Abstracts of Reviews of Effects (DARE)
This is a database of abstracts of quality assessed systematic reviews produced by the Centre for Reviews and Dissemination. DARE can be searched at http://www.crd.york.ac.uk/crdweb/ and its content is also available via the Cochrane Library, TRIP Database, NHS Evidence, OVID’s Evidence-Based Medicine Reviews.
Further information about DARE is available at: 
http://www.crd.york.ac.uk/crdweb/

EMBASE
This is one of the major pharmacological and biomedical databases, containing over 20 million records. The database indexes over 7,000 journals in the fields of pharmacology, pharmaceuticals, toxicology as well as covering clinical medicine, health policy and public health with some coverage of nursing, dentistry, psychology, and alternative medicine. The database coverage includes conference abstracts as well as journal articles.
Further information about EMBASE is available at: 
http://www.info.embase.com/ 
LILACS
A Latin American and Caribbean health research database produced since 1982. It contains articles from @ 670 journals. 
Further information about LILACS is available at:
http://tinyurl.com/yzc3uso

MEDLINE
Produced by the U.S. National Library of Medicine, this database contains over 18 million references. Its subject scope is described as “biomedicine and health, broadly defined to encompass those areas of the life sciences, behavioral sciences, chemical sciences, and bioengineering needed by health professionals and others engaged in basic research and clinical care, public health, health policy development, or related educational activities.” MEDLINE is the largest component of PubMed which is freely accessible at http://www.ncbi.nlm.nih.gov/sites/entrez

Further information about MEDLINE is available at:
http://www.nlm.nih.gov/databases/databases_medline.html

PsycINFO
PsycINFO database covers the literature of psychology and related fields. It includes books, book chapters, and dissertations as well as journal articles.

Further information is available at:
http://www.apa.org/pubs/databases/psycinfo/index.aspx

Science Citation Index Expanded
One of the databases available via Thomson Reuter’s Web of Science service.  SCI covers agricultural, biological, and environmental sciences, engineering, technology, applied science, medical and life sciences, and physical and chemical sciences. One of the key features of this database is cited reference searching.

Further information about Science Citation Index Expanded is available at:
http://isiwebofknowledge.com.

Scopus 
Scopus is an abstract and citation database of peer-reviewed literature and quality web sources with wide subject coverage across the scientific, technical, medical and social sciences literature. As well as journal articles its content includes conference papers, web pages and material from archives and institutional repositories. 

Further information available at:
http://www.info.sciverse.com/scopus/about

Social Science Citation Index
SSCI’s coverage includes economics, education, health sciences, social policy & social work. As with SCI Expanded, one of the key features of this database is cited reference searching.

Further information about SSCI is available at:
http://isiwebofknowledge.com.

Specialist databases

There are many databases covering a particular speciality or area of healthcare and their value will vary from review topic to review topic. Some of these specialist databases available are listed below.

Allied and Complementary Medicine Database
AMED covers complementary and alternative medicine as well as physiotherapy, rehabilitation, acupuncture and occupational therapy.

Further information is available at:
http://www.ovid.com/site/products/ovidguide/ameddb.htm.

BiblioMap
This is the EPPI-Centre database of health promotion research, with @ 14,100 records included. The studies included have been collected from  systematic reviews undertaken at the EPPI-Centre. All studies are tagged by topic,  population group, study type, country etc.

More details from:
http://eppi.ioe.ac.uk/webdatabases/Intro.aspx?ID=7

Educational Resources Information (ERIC)
Covers the education literature including school health, mental health and patient education. Most of its content is journal articles but records of  conference papers, reports and dissertations are also included. Available via a number of different database providers.

Further information about ERIC is available from: 
http://www.eric.ed.gov

Health Management Information Consortium (HMIC)
HMIC contains @ 300,000 records relating to health and social care management with a focus on the UK. It combines databases from the Department of Health’s Library & Information Services and the King's Fund Information & Library Service.

Further information about HMIC is available at:
http://www.ovid.com/site/catalog/DataBase/99.jsp

PEDro
The Physiotherapy Evidence Database is a free database including records of randomised trials, systematic reviews and clinical practice guidelines in physiotherapy. Each entry includes the citation details, an abstract and link to the full text, where possible. It’s produced by the Centre for Evidence-Based Physiotherapy at The George Institute for Global Health.

Further information about PEDro is available at:
http://www.PEDro.org.au/

Social Care Online
A collection of information on social work and social care produced by the Social Care Institute for Excellence (SCIE). It includes research briefings, reports, government documents, journal articles, events and websites.

Further information about Social Care Online is available at:
http://www.scie-socialcareonline.org.uk/

Toxline
This database, produced by the U.S. National Library of Medicine, gives access to information on toxicology, chemicals, pharmaceuticals, pesticides, environmental pollutants.

Further information about Toxline is available from:
http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?TOXLINE

Non-journal literature

The majority of databases described above focus on identifying journal literature. Systematic reviews also need to examine studies published in other formats.

Conference papers and dissertations

Conference Proceedings Citation Index- Science (CPCI-S) and Conference Proceedings Citation Index- Social Science & Humanities (CPCI-SSH) are both  available via Thomson Reuter’s Web of Science. They include reports from conferences, symposia, seminars, colloquia, workshops, and conventions with   a broad coverage of science, technology, social sciences, arts and humanities.

Further information is available at:
http://wokinfo.com/products_tools/multidisciplinary/webofscience/

Dissertation Abstracts
Dissertation Abstracts lists American dissertations accepted at accredited institutions 1861 onwards; Masters theses have been included since 1962; and since 1988, the database includes citations for dissertations from 50 British universities.

Further information is available at:
http://www.proquest.com/en-US/default.shtml

Index of Conference Proceedings
Produced by the British Library, this is available online via The British Library's public catalogue (http://catalogue.bl.uk/).

For further details see:
http://www.bl.uk/bibliographic/nbspubs.html#icp

Conference Papers Index
Available via a number of providers, this database provides access to international research papers and findings presented at scientific and technical conferences and meetings throughout the world.

For further information see:
http://www.cas.org/support/stngen/dbss/index.html.

Another approach to identifying conference proceedings is to scan web pages of relevant professional societies.

Books

Books may provide a useful introduction and overview  of a topic. Some of the largest library catalogues are listed below

British Library Integrated Catalogue
http://catalogue.bl.uk/

Copac ® library catalogue 
A merged online catalogues of many major University, Specialist, and National Libraries in the UK and Ireland, including the British Library. 
http://copac.ac.uk/

Library of Congress
U.S. Library of Congress catalogues containing millions of records.
http://catalog.loc.gov/

New York Academy of Medicine
The NYAM Library is one of the largest publically available collections in the U.S.  The collection includes a substantial amount of grey literature in the areas of public health and health policy. 
http://www.nyam.org/library/

Identifying journals to be handsearched

Systematic reviews frequently involve handsearching of major relevant journals. This is because not all journals are indexed by database producers, and not all indexed journal articles are retrievable from databases. Some databases only index selectively, and some may not index supplements or special issues containing conference abstracts. Relevant journals can be identified from the results of the literature search but the following sources can also be used to identify suitable journals

Ulrichsweb™
Lists over 300,000 serials from around the world including academic and scholarly journals, peer-reviewed titles, newspapers  in all subject areas. 
Available from:
http://www.ulrichsweb.com/ulrichsweb/.

PubMed Journals Database
Searchable by topic, journal title or abbreviation, ISSN, or browsed by subject terms.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=journals

Other sources to search

Internet searches
While the internet can be used to identify primary studies it can also be problematic to search because of limited functionality e.g. not possible to save  search history,  replicate your search results, no facility to download records. All these features are of importance when carrying out extensive searches for a systematic review.

One approach may be to develop a much more focused search using one of the general search engines http://www.google.co.uk/. Check whether there is an advanced search option or other search facilities (phrase searching, field specific searches, Boolean operators etc) that can improve the relevancy of results.

It may be worth trying more than one search engine as you can often get different results from different search engines even when using the same search.

An Internet search can identify websites of relevant organisations, companies, academic centres which can then be scanned for relevant research studies.