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://www.ovid.com/site/catalog/Catalog_DataBase.jsp) also 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 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 a range of methods for identifying studies, how to manage the references retrieved by the searches, obtain documents and write up the search process. Examples of search strategies and search documentation are given. Complementary chapters include advice on issues specific to searching for clinical tests, public health interventions, adverse effects, economic evaluations and qualitative studies.

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.

The Cochrane Database of Systematic Reviews
The Cochrane Database of Systematic Reviews 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/ 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/

CERUKplus
CERUK plus describes itself as “a free, online database of current education and children's services research in the UK". It covers individual PhD studies, as well as long term, large-scale research such as national surveys. CERUK plus is a resource for commissioners and users of research, and researchers currently conducting studies”. http://www.ceruk.ac.uk/index.asp

International register of ongoing systematic reviews
The Centre for Reviews and Dissemination (CRD) is developing an international register of ongoing systematic reviews. The register will use the existing IT platform and infrastructure that supports production and provision of the CRD databases and will be similar to clinical trials registers, prospectively recording key features of systematic reviews in progress. For information about the Register go to: http://www.york.ac.uk/inst/crd/projects/register.htm

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 database of controlled trials that is one of the best available resources for those preparing and maintaining systematic reviews or searching for trials. CENTRAL includes citations that may not be indexed in MEDLINE, EMBASE, or other bibliographic databases, citations published internationally in many languages, and citations that are available in conference proceedings or other hard to access 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 over 54,000 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 on all clinical trials, and the public accessibility of that information. http://www.who.int/ictrp/en/

metaRegister of Controlled Trials (mRCT)
The metaRegister of Controlled Trials ( mRCT) is a searchable, international database of ongoing randomised controlled trials and some completed trials in all areas of healthcare. http://controlled-trials.com/mrct

Centerwatch
Listing of 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://www.ukcrn.org.uk/index/clinical/portfolio_new.html

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.

ASSIA: 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.

Further information about BIOSIS is available at:
http://thomsonreuters.com/content/PDF/scientific/BIOSIS_Factsheet.pdf

The British Nursing Index (BNI)
The British Nursing Index (BNI) is a bibliographic database that indexes 240 UK journals and other English language sources and covers 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)
CDSR is a collection of regularly updated systematic reviews looking at health care and health policy. The CDSR is available as part of the Cochrane Library and is currently freely available in the UK.

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 disciplines such as 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 and SUMSsearch.

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 has recently extended its coverage to include conference abstracts

Further information about EMBASE is available at:
http://www.info.embase.com/

LILACS
LILACS is a database of Latin American and Caribbean health research published since 1982. It contains articles from around 670 journals.

Further information about LILACS is available at:
http://bvsmodelo.bvsalud.org/site/lilacs/I/ililacs.htm

MEDLINE
The MEDLINE database produced by the U.S. National Library of Medicine's contains over 18 million references to journal articles. 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 also covers life sciences vital to biomedical practitioners, researchers, and educators, including aspects of biology, environmental science, marine biology, plant and animal science as well as biophysics and chemistry. Increased coverage of life sciences began in 2000”

MEDLINE is the largest component of PubMed which is freely accessible at http://pubmed.gov/.

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. The database includes books, book chapters, and dissertations as well as journal articles.

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

Science Citation Index
One of a group of databases available via the ISI Web of Knowledge service. ISI Web of Knowledge provides access to ISI Web of Science (Science Citation Index (SCI), Social Science Citation Index (SSCI) and Arts and Humanities Citation Index), ISI Proceedings (Science and Technology edition and Social Science and Humanities edition) and the ISI Journal Citation Reports.

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.

It is available via Web of Science as Science Citation Index Expanded and online as SciSearch.

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

Scopus
Scopus is a large 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, webpages and material from archives and institutional repositories. A subscription is required

More information available at:
http://info.scopus.com/

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

One of a group of databases available via the ISI Web of Knowledge service. ISI Web of Knowledge provides access to ISI Web of Science (Science Citation Index, Social Science Citation Index and Arts and Humanities Citation Index), ISI Proceedings (Science and Technology edition and Social Science and Humanities edition) and the ISI Journal Citation Reports.

Further information about Social Science Citation Index 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)
AMED covers complementary or 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, containing over 14,100 records at present. The studies included in BiblioMap have been compiled over a number of years as a result of searching and coding research for inclusion in systematic reviews at the EPPI-Centre. All studies are coded for specific characteristics of health focus, population group and study type.

Further information about BiblioMap is available from:
http://eppi.ioe.ac.uk/webdatabases/Intro.aspx?ID=7

Educational Resources Information (ERIC)
Covers the literature of education including school health, mental health and patient education. Most of its content consists of journal articles but it also includes sources of grey literature such as conference papers, reports and dissertations. Available via a number of different routes including being freely available on the Internet.

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

Health Management Information Consortium (HMIC)
Published by Ovid, HMIC currently contains over 300,000 records relating to health and social care management with a focus on the UK. HMIC contains the databases of the Library & Information Services of the Department of Health 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
PEDro is the Physiotherapy Evidence Database. It is a free database that includes 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. PEDro is 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
TOXLINE gives access to information in toxicology, including chemicals and pharmaceuticals, pesticides, environmental pollutants. It is produced by the U.S. National Library of Medicine.

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)
These two databases are available via ISI Web of Knowledge and include the published literature from conferences, symposia, seminars, colloquia, workshops, and conventions. There’s a broad coverage of science, technology, social sciences, arts and humanities

Further information is available at:
http://wok.mimas.ac.uk/.

Dissertation Abstracts
Dissertation Abstracts lists American dissertations accepted at accredited institutions since 1861 with a selection of Masters theses being included since 1962. 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
Boston Spa: British Library Document Supply Centre (1964 - ). Available in hard copy as the Index of Conference Proceedings, and 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 potentially relevant conference proceedings is to scan web pages of professional societies.

Books

Books may not only be useful introductions and reviews of a topic, but they can also contain many references to original studies which a review team will want to follow up.

A number of resources give access to some of the largest catalogues in the world:

British Library Integrated Catalogue
Free access to the catalogues of the major British Library collections.
http://catalogue.bl.uk/

Copac ® library catalogue
Gives free access to the 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
A WWW interface to the Library of Congress catalogues, which contain millions of records.
http://catalog.loc.gov/

New York Academy of Medicine
The NYAM Library's Online Catalog contains over 250,000 bibliographic records, representing approximately 85% of the Library's collections. The Online Catalog primarily contains materials acquired after 1972 and the Library's entire journal collection with over 1400 titles. The NYAM collection includes a substantial collection 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 may be clear from the results of the literature search but the following sources can also be used to identify journals to handsearch

Ulrichsweb™
Lists over 300,000 serials from around the world including academic and scholarly journals, peer-reviewed titles, newspapers and other serials in all subject areas.

This database is available from:
http://www.ulrichsweb.com/ulrichsweb/.

PubMed Journals Database
The database can be searched 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
The internet can be used to identify research in progress, research reports, and useful collections but it can also be problematic to search because of limited functionality e.g. it is often not possible to save your search history or replicate your search results, and sometimes there is 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.

Institutional Repositories
Open access to research has grown considerably in recent years so directories and registers can be an efficient way to locate useful resources to search.

Open DOAR is a searchable directory of academic open access repositories.
http://www.opendoar.org/