When developing a systematic search, it’s important to use an iterative approach, constantly tweaking and reevaluating your strategy to ensure relevant articles are captured (and hopefully, non-relevant articles are minimised).
Today, I’d like to share a trick that I frequently use when building my searches. First, develop a set of articles which are relevant to your topic. These are articles which should definitely be picked up by your search. The articles might come from researchers or your patrons, other team members on the systematic review, background scoping searches, google scholar, or any other number of places. The more variety in the set of articles, the better. These articles will comprise your “gold standard set” by which you will test your search strategy.
PART 1: Formatting your PMIDs
First, put each of these articles into your citation management system (ideally EndNote). Next, ensure that each article contains a PMID (PubMed ID) in the accession number field (or whichever one you choose). In EndNote, this can often be easily done by clicking “references”, then “find reference updates”. However, do check through all the citations for any that are missed; it may be necessary to manually find the PMID in PubMed.
After you have your gold set all tidied up in EndNote, export the set of references using a custom output filter containing only the accession number field. To set this up in EndNote v7 (only required the first time you do this!):
- go to Edit -> Output Styles -> New Style.
- in the sidebar, find “Bibliography” heading and click the “Templates” subheading.
- in the box that says “Generic”, click “Insert Field”, then “Accession Number”. Save and close your output filter with a descriptive name such as “PMID”.
To export the references using your new filter, first make sure that your newly created output filter is selected (the name should appear in the dropdown box on the top header; if not select the dropdown box, then “select another style”). Next, press ctrl + A to select all references, then right-hand click and select “copy formatted”.
Open a word document and press ctrl + v to paste your formatted references. Your document ought to contain a list of PMIDs – one per line. From here, I use the find and replace tool to automatically format the list of PMIDs for Ovid Medline:
- Click “find and replace”.
- In the “find what” box, enter ^p (this stands for the paragraph character)
- In the “replace with box”, enter “_OR_” (the underscores represent spaces)
- Press “Replace all”.
Okay! Still with me? Your word document should be formatted most of the way. Now, I finish by adding an open parenthesis at the beginning of the document and replacing the final ” OR sequence with ).ui. The .ui at the end refers to the Ovid Medline field code for accession number (where the PMID is stored). The text of your document should now look something like this:
(“19901971” OR “22214755” OR “22214756” OR “24169943” OR “24311990” OR “18794216” OR “25491195” OR “16931779” OR “9727760” OR “22529271” OR “18757621” OR “25536072” OR “24838102” OR “25025477” OR “23460252” OR “26888209” OR “24381228” OR “25154608” OR “21889426” OR “24165853” OR “25315132” OR “26819213” OR “26936902” OR “27492817” OR “27531721” OR “27522246” OR “27067893”).ui
This process might take a little while to set up the first time, but once everything is automated through your custom output file, it will only take a few seconds in the future. I’m a big fan of front-loading my work to make things easier down the line.
PART 2: Testing your gold standard set
Now, navigate to your draft search strategy in Ovid Medline and paste the full query from part 1 into a new line below the search.
Take the line of your final search results and the line containing your gold standard set and OR them together. If the last two lines in Ovid contain the same number, you’re in luck! All the citations in your gold standard set will be picked up in your draft search. If not, NOT out your original search results to see which ones have been missed; by looking at these citations, you can strategise ways to pick up articles with similar wording or indexing.
I sometimes find that researchers are concerned about whether the relevant articles they have found will be captured by my search strategies, so I sometimes include this “gold standard search” in draft strategies that I send. I also annotate my process to make it more clear.
The beauty of this method is that as new relevant papers are discovered from additional sources, you can add them to the gold standard set, and continually check your strategy throughout the drafting process.