Boolean Logic

Any sophisticated search engine (including PubMed) uses the Boolean logic terms OR, AND and NOT in precise ways to expand or contract a search. In a nutshell the result is that

  • OR is used to expand the search
  • AND to look at the overlapping portions between two searches and
  • NOT to exclude a portion of the search.

Fig 6.3 What Boolean terms mean
A OR B means all of A, all of B including the overlap
A AND B means only the overlap between A and B
A NOT B means all of A except the overlap with B

Note that some of these definitions are not intuitively what you might expect. (Table 6.11)

Table 6.11 Examples of Boolean terms and their meaning

Boolean Term Means Example Means
AND Together with Scaphoid AND Avascular Necrosis AVN of the scaphoid (only)
OR Either/or Osteonecrosis OR Avascular Necrosis Either Osteonecrosis or Avascular Necrosis
NOT Excluding Avascular Necrosis NOT Hip AVN of everywhere except the hip

If you search for Osteonecrosis AND Avascular Necrosis you might expect to get all the sites which refer to Osteonecrosis AND all the sites which refer to Avascular Necrosis. Instead you would get only those sites that refer to BOTH Osteonecrosis and AVN. To increase sensitivity you would use OR. To increase specificity you would use AND and NOT.

Once you have gained familiarity with the PubMed system you may conclude that it just misses formulating the question which you want to ask. What we want to find are the papers which compare pin fixation to another method of treatment using the "gold standard" method of evaluation - a clinical trial. Judging by previous results in this workshop the largest selection of citations comes when you ask for "Colles' fracture" plus "Distal Radius Fracture". To filter that set of citations into the set that matches our requirements we can use the AND Boolean logic operator. If you enter "(Colles' fracture OR distal radius fracture) AND pin AND clinical trial" as the search string you will get eleven papers with an extremely high degree of relevance to the subject. Interestingly there are two sets of duplicate papers in this collection (i.e. the same study published in two different journals!)

*Key Point* Boolean Logic using your own terms is probably the best way to narrow down the search to the "best" paper. However, to get an inclusive collection of papers on the subject you will probably need to use the [See Related Articles] feature associated with that paper.

Saving searches

PubMed used to display the search URL which you could copy and use again later. Now a universal URL something like http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=PubMed is displayed. However, you can find the search URL by

1) clicking on "Details"

2) clicking on the URL button.
pubmedurl.gif (4841 bytes)

3) The search url is then displayed in your browser address bar

and (for the Colles Fracture search) looks like

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=PureSearch&db=PubMed&details_term=%22colles%27%20fracture%22%5BMeSH%20Terms%5D

4) You can save this or bookmark it for use later.

PubMed has its own Tutorial which is more comprehensive than this (but isn't based on orthopaedics). Its goals and objectives are:-

"By the end of this course, you should be able to:

  • Understand PubMed's scope and content.
  • Develop search strategies.
  • Display, save, print, and order search results.
  • Use Limits, Preview/Index, History, and Clipboard features.
  • Link to full-text articles and other resources.
  • Use PubMed services: MeSH Browser, Journal Browser, Single Citation Matcher, Clinical Queries, and Cubby. "

Summary

  • Searches of the Medline Database using the PubMed facility are rapid, easy and give comprehensive results.

  • Framing the correct search term is the critical skill and takes practice.

  • PubMed has some features to help expand your search [See Related Articles], or filter or narrow it. [Clinical Queries]. Although these may be helpful you may prefer to use Boolean logic to frame your own highly specific enquiry.

Other useful parts of the PubMed site

Tutorial -if you need to review this material the tutorial has another slant on it. Much more related to the specifics of using PubMed and less related to framing a search strategy. http://www.nlm.nih.gov/bsd/pubmed_tutorial/m1001.html

List of Journals cited in Medline Journal Browser http://www.ncbi.nlm.nih.gov/entrez/jrbrowser.cgi  

Journals with links to full-text web sites http://www.ncbi.nlm.nih.gov/entrez/journals/loftext_noprov.html

PubMed Help http://www.ncbi.nlm.nih.gov/entrez/query/static/help/pmhelp.html  

PubMed FAQs http://www.ncbi.nlm.nih.gov/entrez/query/static/faq.html  

MeSH Browser http://www.ncbi.nlm.nih.gov/entrez/meshbrowser.cgi  

Clinical Queries http://www.ncbi.nlm.nih.gov/entrez/query/static/clinical.html 

Single Citation http://www.ncbi.nlm.nih.gov/entrez/query/static/citmatch.html 
Useful for finding articles by a certain individual

Loansome Doc http://tendon.nlm.nih.gov/ld/loansome.html
Used to obtain full text copies of the articles.