What is a search filter or hedge?
These are pre-developed search strategies that are developed to define search criteria on a given concept. Filters and hedges are essentially more complex and refined search strings to use in research databases. Many are available online for public use. While filters and hedges are terms often used interchangeably, filters typically refer to static concepts such as study design (i.e. is your search limited to randomized control trials (RCTs)?) while hedges typically refer to subjects (e.g. artificial intelligence).
These can be useful tools to take advantage of in large evidence synthesis projects. When conducting a high-level review like a scoping or systematic review, the filter or hedge may exclude relevant materials. Be sure to double-check before using and ensure it matches your parameters and protocol. Read below for additional information and resources to aid in finding filters and hedges.
Who develops filters and hedges?
Many databases already feature built-in sets of search filters that are commonly used to limit results by age group, publication type, study type, and more. Those filters and hedges found online are typically created and refined by expert researchers and librarians who understand the nuances of controlled vocabulary and database syntax. Filters and hedges may even undergo rigorous testing and validation on top of standard testing through trial and error. It is best practice to cite and/or acknowledge the use of a filter/hedge, particularly if it was formally validated.
What should I look for when choosing a filter/hedge?
- Database/interface: Which database was the filter/hedge designed for? They are not interchangeable! Controlled vocabulary is the overarching concept of using standardized terminology, however databases may use their own controlled vocabulary in addition to a specific syntax. For example:
- Controlled vocabulary: these databases all have different thesauri; Pubmed uses MeSH, CINAHL uses CINAHL Subject Headings, and Embase uses Emtree. See the difference between:
- Pubmed: mental health[MeSH Terms]
- Embase: 'mental health'/exp
- Syntax: a term may be the same or similar across the thesauri, but is represented differently. See the difference between:
- Pubmed: "mental health care access"[Title/Abstract]
- Embase: 'mental health care access':ti,ab
- Date of development and update: Is the filter/hedge current? Search terms and database structure can evolve over time and new terms and concepts can be added, which can impact the performance...and your research.
- Testing/validation: Usually when a filter/hedge is shared online, there will be a note about how it was tested. There may even be a citation and/or link to a published study that validated the filter/hedge and widely disseminated it. Like the date, testing can be an indication of the filter/hedge performance reliability.
https://libguides.sph.uth.tmc.edu/search_filters/ovid_medline_filters