What the heck? The unintended of consequences of misplaced Boolean operators
Regina M Maxwell
Helping Medical Affairs Directors stay on top of the science in your therapy areas with expert literature research and analysis. Medical Literature Research | Literature Management | Copyright Compliance
You’ve got a research question and you’ve done your homework to gather all the synonyms and create your synonym sets. You plug everything into PubMed and you start reviewing your results but something is just not right! There are only a few results for a topic that you know has been the subject of many papers. Assuming that your search terms are on target, and you’ve brainstormed all the synonyms, it sounds like you may have AND-ed some concepts when you should have OR-ed them. ANDing terms narrows your search strategy and decreases the number of results you will retrieve. Very important, where appropriate, but it can cause lots of problems when this operator (or any operator) is misplaced!
For instance, getting back to our original search query, “What are the safety issues around using VEGF inhibitors for neovascular age-related macular degeneration?” and looking at our safety terms:
Synonyms are OR-ed together to form the set. This means that only one of these terms needs to be present in each of the search results. The effect of this is that it (usually) increases the number of results because any of the terms would suffice to make an abstract a match. If we were to AND these synonyms, as in:
this means that all of these terms must present in every abstract. The effect of AND-ing terms is that it limits the number of results and may, in fact, bring back zero results. In our example search query, we primarily use AND to link whole synonym sets so that we get targeted, relevant results.
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The inverse is true when you inadvertently OR in place of AND.
If you were to OR the synonym sets together, as in:
this means that any single one of these terms (from almost the entire search strategy) must appear, but not necessarily in combination with any of the other terms. Basically, a free-for-all, and pretty much meaningless.
As you may have experienced, when you’re creating a complex search strategy it can be quite easy to accidentally AND terms when you'd meant to OR them, or vice versa. That’s why it’s critical to review each component of the search strategy for accuracy so that you’re confident you’re getting exactly what you intend to ask for.