Evidence Based Medicine Guide: Filtering PubMed for the Best Evidence
NLM's PubMed Tutorial
Features and tools especially useful in searching for clinical evidence
Access Clinical Queries
Clinical Queries is linked from the PubMed homepage, in the list of PubMed Tools.
If you have already started searching, you can return to the PubMed homepage at any time by clicking the PubMed logo, on the upper left corner of most PubMed pages.
Article Type Filter Limitation
Article Type filters cannot be used to find the most current evidence.
With the exception of "Systematic Reviews", the filters in the Article Types category are Publication Types, part of MEDLINE's controlled vocabulary. Like MeSH terms, Publication Types are assigned by subject analysts when an article is indexed — weeks, or even months after the record is in PubMed. Using these filters excludes articles that havn't yet been indexed.
Filters allow you to limit your search results by date, article type, and other characteristics. The Article type filter is an excellent way to restrict your search results to the best types of evidence for your clinical question type. PubMed's Clinical Queries tool uses a set of built in search filters to, "limit retrieval to citations to articles reporting research conducted with specific methodologies, including those that report applied clinical research."1
1. PubMed Help Manual - http://www.ncbi.nlm.nih.gov/books/NBK3827/ - Accessed 12/8/14
Article Types Filters
PubMed offers search filters on the left sidebar of search results pages. Article Type selections allow you to specify study characteristics in your search.
Among the Article Types that may be helpful in EBM searches are:
Meta-Analysis: If you wish to find meta-analyses only, use the Meta-Analysis Limit.
Multicenter Study: The "Multicenter Study" limit can help identify research that had larger study populations and, frequently, a wider range of patient characteristics.
Randomized Controlled Trial: This research method provides the best evidence for therapy, prevention and, when available, for etiology/harm questions. (The best evidence for diagnostic studies usually comes from crossover studies, and randomized controlled trials are not usually possible in research on disease prognosis.)
Systematic Reviews: This filter is identical to the Systematic Reviews filter in Clinical Queries.
Only the most frequently used filters are available by default on the search results page — in this screenshot only Clinical Trial and Review are available. Click more... to see the full range of Article Types available.
To learn more about using Filters, see NLM's PubMed Tutorial, linked from the right sidebar of this tutorial.
Clinical Queries allows you to enter one search query and launch two EBM filters: Clinical Study Categories and Systematic Reviews.
Clinical Study Categories are available for five categories: Etiology, Diagnosis, Therapy, Prognosis and Clinical Prediction Guides. (The default search is for Therapy) You can also choose to conduct a Narrow, specific search or a Broad, sensitive search.
The Systematic Reviews filter finds more than systematic reviews. According to PubMed, this filter "is intended to retrieve citations identified as systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine, consensus development conferences, guidelines, and citations to articles from journals specializing in review studies of value to clinicians."
How Clinical Queries Works
Because each question type is best answered by a different study design, unique search algorithms were identified for each category. Clinical Queries automatically employs sophisticated search strategies in the background. By using keywords and truncation in combination with medical subject headings, Clinical Queries is able to retrieve the most current citations in PubMed, including articles that are not yet indexed with MeSH headings and Publication Types.
- View the Systematic Reviews filter search strategy here.
- The search strategies for the Clinical Study Categories filter are listed here.
To learn more, view the NCBI PubMed Tutorial's unit on Clinical Queries. You'll find links to the tutorial on the right sidebar of this page.
Getting the Most from Clinical Queries
The Systematic Reviews filter is designed to find all high quality "consensus development" papers. Because it is optimized to provide comprehensive results, it sometimes retrieves lower quality narrative reviews (especially if they have the phrase "evidence based" in their title).
The majority of systematic reviews and meta-analyses have been done on questions of therapy. To use Systematic Reviews to find evidence on other question types, you may need to add additional search terms to your search. For example, to find a systematic review of a diagnostic test, you might add (AND) the search word "specificity" to your query.
The table here, although certainly not exhaustive, provides search terms that we have found useful for identifying systematic reviews and meta-analyses for questions other than therapy. The single most useful term is bolded. The asterisk (*) is a truncation symbol in PubMed; when an asterisk is added to the the end of a word, PubMed looks for variations of the word (e.g., diagnosis, diagnoses, diagnostic, etc.).
|Search Words to Filter for Question Type|
Prevention; Primary prevention
Prognos*; Natural History
Clinical Study Categories
- Use the therapy category for studies of prevention as well as therapy.
- It is often helpful to add the search terms "prevention" or "primary prevention" to your query to find studies that are primarily about preventing rather than treating a disease or condition.
- Use the etiology category for questions of harm as well as causation.
- It may be helpful to add search terms such as "harm" or "adverse effects" to your query to find studies about harmful effects of interventions intended to be therapeutic.