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PubMed Advanced Interface - IV. Viewing Search results

When you press go on the Preview/Index screen PubMed executes your search and produces a list of citations. In addition, a toolbar is provided which offers useful facilities. One of these is the Details button, which allows you to see your exact search string. It is a good habit always to look at this string before accepting your list of citations. Not only does it allow you to check that your search is correct, but it is also educational in learning PubMed syntax. Furthermore, if you search PubMed frequently, you can copy and paste this search string into a text document, so that you can use it at a future date.

Figure 6. List of Citations

In the example above we are looking at the 21,039 results obtained from typing "multiple sclerosis" into the PubMed search box and pressing Go. PubMed has had no problems in mapping your term to MeSH, and it therefore operates its default search. If you click on Details, you will see that the actual search executed is: -

("multiple sclerosis"[MeSH Terms] OR multiple sclerosis[Text Word]) AND notpubref[sb]

PubMed is actually a subset of a larger database called PubRef, which indexes a broader range of scientific journals.  PubMed searches exclude PubRef citations unless you delete the "AND notpubref [sb]" from the PubMed Query box and click Search (alternatively you can specify a PubRef search when you use the Limits screen).

You can see that PubMed has executed the single string "multiple sclerosis" as both a MeSH search and a textword search and combined them with the Boolean OR. PubMed will perform this combination routinely, provided the term you enter is a valid MeSH term. It will not perform the combined MeSH/textword search if you execute the search from the NLM MeSH Browser screen, even though you may have found a valid MeSH term on that screen.

One feature of PubMed, which is often very useful is the Related Articles facility. if you look at Figure 6, you will see a small hyperlink to the right of each citation. When you click on this, PubMed executes a search to find articles which are thought to be closely related to the one you selected.

Explode and Focus

By now, particularly if you have used Medline before with the Ovid interface, you may be wondering about how to "Explode" and "Focus" MeSH terms.

"Explode" combines all of the "children" of your selected subject heading with the Boolean OR operator. This ensures more complete coverage (sensitivity). In fact, PubMed performs the explode function automatically, which is a sensible option for most searches. If you don't want your term exploded (because none of the children of the term are relevant) you will have to switch it off. This is done by using the syntax "Multiple sclerosis"[MH:NOEXP].

"Focus" is a judgement made by the Medline Indexer that the selected MeSH heading is the main concept of the article. The PubMed equivalent to Ovid "Focus" is to use the MAJR field, as in "Multiple sclerosis"[MAJR]. This increases specificity (at the expense of sensitivity). My recommendation for an initial search is to allow PubMed to automatically explode all of the relevant MeSH terms, but not to focus. If you find too many results you can rerun this part of the search with the MAJR option.

The Subject Search

At this stage you should be able to execute a good quality subject search, which you will then combine with a systematic (EBM filter) search.