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Put your clinical question into the PICO format:
- Population/Patient Problem: Who is the patient population? (disease of, health status, age, race, sex)
- Intervention: What is the intervention? (therapy, medication, treatment)
- Comparison: What is the reference group which is being compared with the treatment intervention? (different type of treatment, no treatment)
- Outcome: What is the outcome that is being measured? (less symptoms, no symptoms, full health, decreased mortality, etc.)
Brainstorm and jot down keywords for each part of your question. Try to think of every possible way an author/researcher might refer to your topics. Cross out words that aren't working and add to this list as you search.
Keep a search log or print your search histories. This will keep you from re-running the same searches and help you track how you've had to adjust your search.
This 4-minute tutorial explains how to use Boolean operators (AND, OR, and NOT) to build a search statement. (Click the button in the bottom right to expand the tutorial to full screen.)
Use an asterisk (*) after the root of a word to search for variant endings. For example, stretch* will find stretching, stretch, stretches, etc. This is called truncation.
Use quotation marks to keep words together as a phrase (e.g. "heart attack").
Look at the "help" menu in each database for more searching tips.
Levels of Evidence and Article Types
The American Occupational Therapy Association (AOTA) defines 5 levels of evidence when appraising research studies for evidence-based practice. The AOTA's EBP Project created the Guidelines to Critically Appraised Paper (CAP) Worksheet which provides the Levels of Evidence table and descriptions of the various study designs at each level.
You want to be certain to search in the relevant databases for your topic and for the level of evidence you need. Look at the descriptions of each database in this guide to decide databases which will help you find the type of articles you need. Be thorough by searching in more than one database.
Note: Don't be surprised or discouraged if you don't find higher levels of evidence on your topic. This can be a result of the newness of the particular topic and how much attention the research community has given to the topic.
Search Terms: Keywords vs. Subject Headings
With a project such as the Critically Appraised Topics (CAT) assignment which involves comprehensive literature searches, it may be helpful to understand the difference between keywords and subject headings and the differences when searching with each.
- Keywords are any words that appear in the database record for an article, typically including the article title, abstract, journal title, subject terms, authors, author's affiliation, etc.
- Before searching, brainstorm to come up with a list of keywords and phrases to describe your topic.
- Searches using keywords are fast and easy and, for normal searches, may lead you to sufficiently relevant articles.
- However, keyword searches will also retrieve articles that are not truly about the keyword search terms used; the terms may only be mentioned once in the article or may be used in a different context than you intended (e.g., AIDS will also retrieve articles on hearing aids, audiovisual aids, clinical aids, teaching aids, etc.)
- Subject headings/terms are standardized terms that are added to the database records of articles by professional indexers who have read each article to determine what each is truly about.
- These standardized terms consolidate different words used to describe the same concept (e.g., teen, teens, teenager, adolescence, etc.) into one standardized term (e.g., Adolescent)
- Subject headings/terms are called a variety of things, depending on the database: Descriptors, MeSH Terms (Medical Subject Headings), CINAHL Headings, Index Terms, Controlled Vocabulary, etc.
- Searching by subject headings/terms will often yield a more focused set of results because your search is limited to the relevant subject(s)
- Subject headings/terms are hierarchical, which makes broadening and narrowing a search much easier
I recommend that you try both types of searches. Start with keywords, notice the subject terms found in relevant results, and then use these subject terms to set up more focused searches. There is no one-way to search; it is an iterative process, whereby you try one search, make discoveries which will further direct the next search, and so-on. Some searches may be all keywords, some all subject terms, and some a combination of both. Here's an example of a search in PubMed, that uses a Medical Subject Heading and a keyword phrase:
Child Development Disorders, Pervasive[MeSH] AND "therapy ball chairs"
Broaden or Narrow Your Search
When you can't find any or enough information or when the studies you're finding are of lower-than-ideal quality, try some of these tricks for broadening your search:
- Try using synonyms for your original search terms
- Explore related or broader topics (e.g., exercise therapy instead of stretching). Don't forget that you can refer to PubMed's or CINAHL's subject headings tree/hierarchy to see what the next broader term is
- Remove less critical search terms from your search
- Expand the date range and/or population
- Consider doing a keyword search instead of subject heading search
When you are getting large numbers of results, try some of these tricks for narrowing your search:
- Add additional search terms to your search statement using AND
- Explore limit options or filters in the database (e.g., date range, publication types, age range, etc.)
- Focus on a specific aspect of your broader question. Don't forget that you can search by subject term subheadings (e.g., adverse effects, rehabilitation, therapy, etc.).
- If your initial search was a keyword search, try a subject heading search instead
- Limit to articles where your subject headings are a "major" focus (using PubMed's MeSH Database or CINAHL's "CINAHL Headings" look-up)
- If you are doing a keyword search, search for terms only in the Title or Abstract