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Evidence-based Medicine Resource Center
Fact Sheet

THINGS TO KEEP IN MIND WHEN SEARCHING MEDLINE

by The Librarians' Working Group

1. Successful EBM searching involves formulation of a focused clinical question. Phrasing a specific, answerable question can help searchers conceptually envision a search and choose vocabulary to express strategy.

2. Regardless of the MEDLINE interface, searching will involve subdividing a larger topic into concepts. There are many ways to express search concepts including the use text words or free text; or, Medical Subject Headings, or Tree Explosions which allow you to search for broader and/or more specific headings at the same time. Subheadings help to focus the search. Free text and controlled vocabulary searching can be combined.

3. Free text searching is a fine and dandy way to search most MEDLINE interfaces. In fact, it is sometimes the only way to search for a particular concept. Keyword searching relies on the author's use of words in the title and/or abstract. For maximum retrieval, use several different words and acronyms that express the concept.

4. Different MEDLINE interfaces vary when searching free text terms. Some search each field in the entire record. Some search only in selected fields of the record. Some interfaces map free text terms to a corresponding Medical Subject Heading. Become acquainted with what interface is doing behind the scenes. When in doubt, ask a librarian!

5. Subject heading searching (AKA, thesaurus searching, or controlled vocabulary searching), can be an efficient way of finding information. Remember to use the most specific heading available to describe the concept. If the search interface has a built-in thesaurus to help locate and use subject headings, don't be shy about using it.

6. More than 70 subheadings are available, and can be used to refine the search. There may be more than one subheading which expresses an EBM concept. Example: for a therapy search, the subheadings: therapy, radiotherapy, surgery, drug therapy, or diet therapy could be used. Use subheadings judiciously. They can help to refine your search, but if too many subheadings are applied, the retrieval may be severely limited missing the information you need.

7. Searching for methodological terms - or narrowing to a particular type of study - can be tricky. In MEDLINE, terms describing epidemiologic study designs can be expressed as subject headings (e.g., cohort studies, case control studies), or as publication types (e.g., randomized controlled trial, multicenter study). Some methodology terms can be both subject headings and publication types (e.g., meta-analysis). In some MEDLINE interfaces, keywords will search all fields simultaneously. However, other interfaces require the use of several strategies at once - e.g., limiting to publication types, entering keywords, and/or using subject headings.

8. Be cautious when using hedges, or pre-assembled search strategies which have been widely published in print and cyberspace. They can be useful, but one size definitely does not fit all. Know how the hedge is operating in your MEDLINE interface so that it can be easily adapted if the strategy does not initially get the desired retrieval.

9. No matter which MEDLINE interface you use, your search will involve combining concepts with Boolean operators (AND, OR). However, when it comes to combining terms, all MEDLINE interfaces are not created equal. Be aware that some interfaces require these logical operators. Some enter them automatically. This "user-friendly" feature can actually be "user vicious"; if you are not familiar with exactly how the system is combining conceptual terms, an odd retrieval that does not meet your needs might be the end result.

10. No matter which interface used, less is often more. The more concepts included in your search, the narrower the retrieval will be. This can sometimes focus your retrieval, and save you the trouble of fishing through hundreds of irrelevant articles. However, you can also restrict your retrieval too much. Obtaining a manageable, relevant retrieval is a skill which comes with practice. Rule of thumb: begin with two concepts, and then add more concepts to narrow.

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Updated: 11/2/98
Patricia E. Gallagher