Narrowing the Search

This subject has been covered in various of the focused workshops. This section summarizes various techniques which can be used to narrow the search. We will assume that you have designed a search string which produces a comprehensive list that covers the subject. The techniques we will discuss for narrowing down the list include

• MeSH
• Major subject
• Limits
• MeSH subheadings
• Free form Boolean terms

History

Because the search string may get very complex it can be good idea to use the history function to make things as simple as possible.

We will use the AVN search as an example and narrow it down to Sugioka Osteotomy for AVN of the femoral neck. You may recall that the largest collection obtained on that subject was using the string

osteonecrosis OR avascular necrosis OR aseptic necrosis

Open the History function by clicking on History.
If there as any previous history (that you don't care too much about!) clear it
Run your search again so that it is Search #1

From now on you can use #1 as your search string in combination with other terms instead of having to copy out the whole thing.

If you are going to want to store the search either don't use history, or translate it back into a string of words when you have finalized your search. The history number will not carry over between different sessions

Most often you have used MeSH terminology to create the inclusive list. Even if not it is probable that PubMed has invoked MeSH terminology in the translation of your search string.

If you haven't yet come across "MeSH term" I suggest reading the workshop on assembling a comprehensive list which gives the fullest treatment of the MeSH system.

You can see this by checking out details
Sure enough Osteonecrosis has been interpreted as a MeSH term

Open the MeSH Browser and enter Osteonecrosis

Scroll down to examine the tree of MeSH terms. Femoral head necrosis is even more specfic. Click on the link to this MeSH term.

The search using this MeSH term will be used instead of Search #1

Major Subject

We only want papers in which AVN is the major subject.

Click on the detailed display link to see the detailed display on Femoral Head Necrosis. The subheadings applicable to MeSH terms are displayed. For now we only want to click on "Restrict Search to Major Topic" and "Do not Explode" since we are not looking for papers about Perthes Disease Click on the Add button

This displays the search string Click on PubMed Search

We have narrowed down the list significantly by using these terms but there is still a large list involved.

Limits

Some further narrowing can be done by using the Limits function. Click on the Limits button (under the text box)

Using the drop-down menus on the limits page set the limits to Only items with abstracts English Human From 1975 After you have entered the limits click on Go

This halves the number of citations

Revisit the History function. While preparing the workshop this search was #5 for me.

MeSH Subheadings

Surgical procedures, including osteotomies, are included as MeSH terms. This is helpful in the current situation.

Click on the MeSH Browser again and enter Osteotomy. Click on detailed display

Click on the checkboxes to select interesting aspects of the procedure. Include Restrict Search to major headings again

Click on Add.

In the textbox which shows the collection of terms which has just been generated type #5 AND to include the search previously completed on AVN

then click on PubMed Search

This particular collection of subheadings produced a list of 68 papers on the subject of osteotomy. However Sugioka's original 1978 paper was not in the list (I am not sure why!). To make sure all the papers on Sugioka Osteotomy were in the list I used the search string "#6 OR (Sugioka AND osteotomy)" where #6 is the search described above. This search (#10 in my history) yielded 99 papers and did include Sugioka's original paper.

Free form Boolean Terms

Out of this collection I thought it would be interesting to assemble the papers that Sugioka himself wrote on this subject. The search string was "#10 AND sugioka y[auth]" and it lists 12 papers, including ones he wrote about osteotomies in other bones.

Summary

Narrowing a PubMed search can be done in a number of ways

• Using a more specific MeSH term

• Defining one or more MeSH terms as Major Subject [majr]

• Using Limits

• Using MeSH subheadings

• Using your own Boolean AND and NOT terms

Myles Clough mylesclough@shaw.ca
Clinical Instructor, Department of Orthopaedics, University of British Columbia
B.C. Canada
Feedback, Comments and Questions welcome.