Guidelines and standards

Search filters and hedges overview

The terms "search filters" and "hedges" are used interchangeably throughout this guide, however there is a slight difference between the two: search filters refer to methods that refine static concepts, such as study design, whereas hedges deal with subject materials. Depending on the research topic, you may be able to save time in constructing your search by using specific search filters (also called canned searches, clinical queries, or optimal search strategies). Search filters usually include a series of pre-elaborated keywords/phrases plus subject headings for a given concept, idea, or study design to find literature within a particular database, e.g., for the MEDLINE database on a given concept.

Watch this video from Yale University for an introduction to pre-made search strategies and suggestions of where to find validated hedges.

Key points from the video

• Building systematic search strategies is complex and time consuming.
• It can be worth searching for pre-made search strategies that match your concepts.
• Pre-made search strategies are known as 'filters' or 'hedges'.
• They may also be called 'optimal search strategies', 'quality filters', or 'clinical queries'.
• Topic hedges are designed to find resources relevant to a specific topic.
• Methodological hedges are designed to find specific study design types.
• These can save time, but there are things to consider before deciding to use existing hedges.
• Some hedges are expert informed, using scientific validation techniques.
• Validated sets have been examined to determine their sensitivity and specificity.
• If a hedge has a sensitivity of 99%, it will retrieve 99% of all articles known to be relevant in a gold standard test set.
• A hedge with high sensitivity will be very comprehensive, but will require you to filter out some irrelevant results.
• If a hedge has a specificity of 99%, it filters out 99% of articles that are known to be irrelevant in the gold standard test set.
• A hedge with high specificity will be extremely focused, but may miss some relevant results.
• In most cases, you will end up choosing a hedge that has a balance of sensitivity and specificity.
• Not all hedges are validated - this doesn't mean they are poor quality, but you will have to carefully evaluate the hedge yourself.
• If a hedge has been validated, consider:
  • the sensitivity and specificity score
  • the database used for validation
  • if you will need to remap the hedge to other databases
  • the subject area of the gold standard test set
  • the date of the validation

 Make an appointment with a librarian for help identifying relevant filters for your search. 

Sources of filters/hedges

Below are links to some commonly used filters you may find useful.

• Pubmed Clinical Queries  Enter your search term and your results will be automatically categorised into Clinical Study Categories, Systematic Reviews and Medical Genetics. 
• CINAHL Clinical Queries allow the user to limit searches using specific search strategies to aid in retrieving scientifically sound and clinically relevant study reports indexed in CINAHL databases.
• CADTH Database Search Filters

  A list of commonly used filters from the Canadian Agency for Drugs and Technologies in Health (CADTH). Note that these filters have not been validated against a gold standard set of articles, and should probably not be used for a systematic review, but maybe useful for other types of reviews.

• Cochrane Handbook, part 2, chapter 4, section 4.4.7: Search filters

  Includes filters to identify randomised controlled trials in a number of databases

• The ISSG search filter resource (InterTASC Information Specialists' Sub-Group)

  '...lists known filters of interest to researchers producing technology assessments' - multiple categories, for example adverse effects; age groups; guidelines; qualitative research; systematic reviews; quality of life

• Search filters - SIGN (Scottish Intercollegiate Guidelines Network)

  Filters include: systematic reviews; randomised controlled trials; observational studies; diagnostic studies; economic studies; patient issues

• Strings Attached: CADTH's Database Search Filters

  Canadian Agency for Drugs and Technologies in Health. Filters include: systematic reviews/meta-analysis/health technology assessment; randomised controlled trials; guidelines; economic evaluations/cost/economic models; health utilities/quality of life; narrow economic filter

• Flinders Filters (Flinders University) (including CareSearch filters)

  Includes: Integrated care; Bereavement, Grief and Loss; Contraception; Dementia; Opthalmology; Heart Failure; Aboriginal and Torres Strait Islander Health; Lung Cancer; Palliative Care; Primary Health Care; Residential Aged Care; Stroke

• Expert Searches - Ovid Tools & Resources Portal (Wolters Kluwer)

  A range of search filters for use in MEDLINE and Embase - primarily focused on current health topics, diseases, and treatments. Most are not validated

• Topic search filters: a systematic scoping review (R. Damarell et al.)

  This scoping review identifies 58 filters across a range of topics. Damarell, R. A., May, N., Hammond, S., Sladek, R. M., & Tieman, J. J. (2019). Health Information & Libraries Journal, 36(1), 4-40. https://doi.org/10.1111/hir.12244

• Hedges - Health Information Research Unit (HIRU), McMaster University

  Filters include: therapy, diagnosis, review, prognosis, causation (etiology), economics, cost, clinical prediction guides, qualitative

• Methodological Search Filters - CEBMa (Center for Evidence-Based Management)

  Filters include: meta-analyses and systematic reviews; controlled and/or longitudinal studies

• BMJ Clinical Evidence Study design search filters

• CareSearch Search filters for palliative care, heart failure, dementia, residential aged care and dementia.

• McMaster / Health Informatics Research Unit Hedges  Search filters or hedges to improve retrieval of scientifically sound and clinically relevant study reports from large, general-purpose, biomedical research bibliographic databases including MEDLINE, EMBASE, and PsycINFO.