UCC Library: Nursing and Midwifery: Search Strategy

Sensitivity vs precision

The goal of systematic review searches is to identify all relevant studies on a topic. Systematic review searches are therefore typically quite extensive. However, it may be necessary to strike a balance between the sensitivity and precision of your search.

Sensitivity – the number of relevant results identified divided by the total number of relevant results in existence.
Precision - the number of relevant results identified divided by the total number of results identified.

Increasing the comprehensiveness of a search will reduce its precision and will retrieve more non-relevant results. However, ... at a conservatively-estimated reading rate of two abstracts per minute, the results of a database search can be ‘scanread’ at the rate of 120 per hour (or approximately 1000 over an 8-hour period), so the high yield and low precision associated with systematic review searching is not as daunting as it might at first appear in comparison with the total time to be invested in the review. (Cochrane Handbook for Systematic Reviews of Interventions, 2008, Section 6.4.4)

See also: IOM Standards for Systematic Reviews: Standard 3.1: Conduct a comprehensive systematic search for evidence

Issues to consider when creating a systematic review search:

All concepts are included in the strategy
All appropriate subject headings are used
Appropriate use of explosion
Appropriate use of subheadings and floating subheadings
Use of natural language (text words) in addition to controlled vocabulary terms
Use of appropriate synonyms, acronyms, etc.
Truncation and spelling variation as appropriate
Appropriate use of limits such as language, years, etc.
Field searching, publication type, author, etc.
Boolean operators used appropriately
Line errors: when searches are combined using line numbers, be sure the numbers refer to the searches intended
Check indexing of relevant articles
Search strategy adapted as needed for multiple databases

Dissertations & Theses

Electronic Theses Online Service (EThOS) A single point of access for theses produced at higher education institutions across the UK. Run by the British Library.

Trials Registers

CenterWatch Global source for clinical trials information, offering news, analysis, study grants, career opportunities, and trial listings to professionals and patients.
ClinicalTrials.gov A registry and results database of federally and privately supported clinical trials conducted in the United States and around the world.
Cochrane Central Register of Clinical Trials CENTRAL is comprised of Specialized Registers from many Cochrane review groups, relevant records retrieved from MEDLINE and EMBASE, and records retrieved through handsearching.
EU Clinical Trials Register Information on clinical trials in EU member states and the EEA and clinical trials which are conducted outside the EU/EEA if they form part of a paediatric investigation plan.
ISRCTN Register The ISRCTN is a simple numeric system for the unique identification of randomised controlled trials worldwide. The ISRCTN Register also accepts registration of other forms of studies designed to assess the efficacy of health-care interventions.
UK CRN Study Portfolio Comprises studies from across England, Scotland, Northern Ireland and Wales.
WHO International Clinical Trials Registry Platform Provides a central database for searching many national trial registries.

Other registries are available and may be worth consulting depending on your subject.

Planning your search - what to include

Where to search

The search strategy must be comprehensive, hence a number of scholarly databases should be searched. Which databases you choose will depend on the topic of the review.

The databases listed below are usually the key databases to search for any systematic review:

Systematic search strategies

Systematic Search Strategies

Systematic searching interactive lesson

Why Should You Use Grey Literature?

The term grey literature "is usually understood to mean literature that is not formally published in sources such as books or journal articles" (Lefebvre et al. 2011, section 6.2.1.8). Grey literature may include research reports, conference papers, dissertations and theses, clinical trials, government documents, census data, standards, patents, and other research outputs.

Grey literature has traditionally been considered somewhat difficult to locate, but it is important to consult these unpublished studies to reduce the risk of publication bias in results.

Reference: Lefebvre, C., Manheimer, E. and Glanville, J. (2011) 'Searching for studies' in Higgins, J. P. T. and Green, S., eds., Cochrane handbook for systematic reviews of interventions [online], Version 5.1.0, available: http://handbook.cochrane.org/ [accessed 19 Dec 2014].

General Resources for Grey Literature

CogPrints An electronic archive for self-archive papers in any area of Psychology, Neuroscience, and Linguistics, and many areas of Computer Science.
Google Try a general search of Google or Google Scholar (http://scholar.google.com/) using your keyword search strategies. You can also use Google Advanced Search (http://www.google.ie/advanced_search) to limit your search to certain domains and by certain filetypes like PDFs.
Grey Literature Report Bimonthly publication of The New York Academy of Medicine Library alerting readers to new grey literature publications in health services research and selected public health topics.
GreySource - GreyNet.org GreySource provides examples of grey literature to the average net-user and in so doing profiles organizations responsible for its production and/or processing.
Mednar A federated search engine that conducts real-time searching of peer-reviewed medical resources.
National Technical Information Service (U.S.) Largest central resource for U.S. government-funded scientific, technical, engineering, and business related information available today.
OAIster A union catalog of millions of records representing open access resources (theses, technical reports, research papers, etc)
OpenDOAR OpenDOAR is an authoritative directory of academic open access repositories.
OpenGREY Open access to 700.000 bibliographical references of grey literature produced in Europe. Covers Science, Technology, Biomedical Science, Economics, Social Science and Humanities.
Science.gov Gateway to government science information and research results from the U.S.
World Health Organization WHO is the directing and coordinating authority for health within the United Nations system. This website houses reports, data and publications from the WHO.
WorldWideScience Global science gateway comprised of national and international scientific databases and portals.