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Search the Literature: Tips and Tricks

Using Limits (Filters) to drill down

Anybody who has ever shopped online has probably used the commercial website equivalent of Limits. They will often appear on the left sidebar in a column labeled "Narrow Your Results", "Filter By", "Shop by Category", or some variation thereof.

Limits can be extremely helpful in developing an efficient, focused search. But here's the trick: apply them in stepwise fashion in order of importance, rather than all at once. That way, if you end up with too few results, you can always remove them one by one.

Suppose you conducted a search in Ovid MEDLINE to find clinical trials that evaluated the use of pneumococcal vaccines in elderly women.

Your search strategy might look something like this:

In this scenario, you first ran a search on the appropriate MeSH heading, Pneumococcal Vaccines. Then you applied Limits for the most essential criteria, English language and Humans.

Next, you applied the Limit for Female, followed by the Limit for people ages 65 and over. When that brought up a sizeable set of results, you then tried the more restrictive age limit, for people ages 80+, which produced 554 results.

Next, you applied the Limit for All Clinical Trials, of any type. When that brought up a fairly good-sized number, you limited that set to Randomized Controlled Trials (RCTs), ending up with 47 results.

What if you didn't t find what you were looking for in those 47 results? Well, you could always back up a step and look at the results in Set 6. And if you still didn't find what you were looking for, you could go back to the broader age group of 65 and over (Set 4), and limit that set to RCTs. When you do that, you've expanded your set to 107 results.

How Limits can help you

When searching the health sciences databases, especially MEDLINE, CINAHL, and PsycINFO, the following concepts are almost always searched via the use of Limits:

  • Age groups
  • Sex
  • Species: Humans vs Animals

Other Limits that can be very helpful include:

  • In Ovid MEDLINE
    • Publication Types, including everything from letters, interviews, and news to randomized controlled trials, meta-analyses, and systematic reviews
    • Subject and Journal subsets
    • Clinical Queries
    • Research Article
    • Exclude MEDLINE
    • Peer-reviewed
    • Any Author is Nurse
  • In PsycINFO
    • Books or Dissertations
    • Methodology