UCC Library: Radiography: 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: