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How to search in the Health Sciences

Filters, Limits and Hedges

The words "Filters" and "Limits" are often used interchangeably in article databases.  Librarians often use "Filters" and "Hedges" interchangeably.  It's important to understand what these terms are referring to in the context of the specific database you are using.  For example:

  • CINAHL = Limits
  • PubMed = Filters

Both of these refer to aspects which are predefined in each database that can be used to focus a search (see Limits basics below).  Search filters (or hedges) "are standardized strategies that help identify literature within specific databases. Using a comprehensive collection of search terms, designed by topic, study design or other features, search filters may be useful in developing your search and allow you to search more effectively." 

University of Alberta Sperber Library. Health Sciences Search Filters: How to Use Search Filters. 2024,

In some cases these are validated or have variations based on the degree of sensitivity or specificity required in a search.  See some examples of basic search hedges used to locate evidence based practice articles below (see also External sources for filters or hedges).  

Limits Basics

The words "Filters" and "Limits" are often used interchangeably in article databases.  They are predefined and used to help refine search results in different ways. Typical limits include:

  • Date Range (e.g. last 5 years)
  • Language (e.g. English only)
  • Article Type (e.g. review articles)
  • Full Text (full text of the article is available)

Some databases offer additional limits, i.e. age groups. See the database Help pages under Limits for full list of limits.

Caution: apply limits at the end of your search. Applying some limits at the beginning of the search, i.e. date range, can eliminate helpful articles from your results.

Evidence based searching using domain hedges

Question type or Domain

Every searchable clinical question falls into a category known as the "type of question" (or domain). Each question type is associated with specific research methods and designs, understanding the question helps identify the research methods and designs you want for your filter. There are many types of questions, in health the main ones are:

  • therapy
  • diagnosis
  • prognosis
  • etiology
  • feeling/experience (qualitative studies)

Evidence based domain hedge examples

Copy and search the appropriate hedge and add it to your topic search using AND. 

The following are basic filters can be used for evidence-based searching:

  • Therapy: “randomized controlled trial” OR “clinical trial” OR (double AND blind*) OR random* OR placebo*
  • Diagnosis: (sensitivity AND specificity) OR diagnosis OR “diagnostic use” OR (predictive AND value*) OR reliability OR validity 
  • Prognosis: incidence OR mortality OR “follow-up studies” OR prognos* OR predict* OR course 
  • Etiology: “cohort studies” OR risk OR (odds AND ratio*) OR (relative AND risk*) OR (case AND control*)
  • Qualitative: ethnography OR phenomenology OR grounded theory OR focus group OR narratology OR qualitative research OR "case study" OR participatory action research 

To use these hedges requires a basic understanding of: