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Systematic Reviews

Keyword vs. Subject Searching

Controlled vocabularies (such as the MESH subject headings used in Medline and EMTREE subject headings used in EMBASE) provide an organized approach to the way knowledge is described.

Their use is extremely important as they bring uniformity to the indexing of publications included within a database. Using the same terminology throughout a database creates consistency and precision and helps you to find relevant information no matter what terminology the author may have used within their publication.

Indexing has traditionally been a manual process, although machine indexing is becoming more prevalent.. Databases such as MEDLINE employ specially trained indexers to read the full-text of each publication then identify all of the concepts covered within the article. These concepts are then translated to the controlled vocabulary used within the database. It is the indexer’s job to ensure that each concept included in the article are identified and assigned a term.

Each database may use different subject headings to describe the same concept. As an example, the term “complementary medicine”:

The MeSH heading (MEDLINE) is "complementary therapies"
The Emtree heading (Embase) is "alternative medicine"
The CINAHL heading is "alternative therapies"

The OVID (MEDLINE),, and CINAHL databases provide a search option to “explode” terms. PubMed automatically explodes terms, although there is the option of choosing not to explode a term. Exploded searches retrieve indexed records for a term, plus other terms which are a derivative (more specific, narrower terms) of the search term. Exploding search terms provides a fast way to find related concepts in a single search.

For example, if a search for “complementary therapies” in MEDLINE was exploded:

The search results would also include records  indexed with the MESH headings acupuncture”, “anthroposophy”, “auriculotherapy”, and so on.

NOTE: Clicking on a MESH heading will display its tree, including the exploded terms.

Complementary Therapies                
                       Acupuncture Therapy            
                       Cupping Therapy                
                       Diffuse Noxious Inhibitory Control                
                       Dry Needling                
                       Holistic Health                
                       Horticultural Therapy                
                       Integrative Oncology                
                       Medicine, Traditional                
                       Mind-Body Therapies                
                       Musculoskeletal Manipulations                
                       Sensory Art Therapies                
                       Spiritual Therapies

Keyword searches are extremely important when conducting systematic reviews, and should be used in combination with the relevant subject headings within each of your database searches: