Boolean Connectors

The rule of thumb in teaching PubMed has always been to teach people to capitalize the Boolean operators (AND, OR, NOT).

But, something interesting happened to me lately. Has this ever happened to you? You’re teaching a PubMed class and in order to impress upon your students the necessity of capitalizing the Boolean connectors, you do a search such as this one:

And then, you compare the number of items retrieved from that first search to this search with the Boolean operators in lower case:

And then you stand there, completely surprised by the results. (Which is yet another reminder that you should check all your sample searches before you use them in class.)

On the day this was written, here’s what happened with both of those searches:

Both searches retrieved the same number of items. And not just the same number of items, the two searches retrieved the exact same citations.

So, what gives? Do we not have to capitalize Boolean operators in PubMed? Are we finally freed from the tyranny of having to put the caps lock on?

Whoa, there. Let’s not jump to conclusions.

Just because the lower case Boolean operators work in one search situation does not automatically mean they will work equally well in all search situations.

The National Library of Medicine has been working on resolving this issue and, as you can see, in some cases it’s apparently true that it does not matter whether you use capital letters or lower case letters for those three little words.

However, NLM assures me that there are situations where lower case Boolean operators do not work properly. Personally, I haven’t come across any, so I have no examples to share with you. But, I believe them when they tell me this because I’m sure they would be just thrilled to be able to tell folks they no longer have to worry about using upper case letters for Boolean operators.

So, where does this leave us?

It is recommended that we continue to teach people to use caps for connecting words. Big letters for Booleans, please.

Do not change your instruction until you get a clear indication from NLM that lower case Boolean operators work all the time, in all search situations.

And then, perhaps, we can rest a bit easier knowing that when our learners forget what we’ve taught them, there is a high probability that they will get useful results anyway.