Out of the common library statistics, I think reference questions and program attendance most highly correlate to User Experience. It may be possible to correlate circulation statistics to UX, but it would be more difficult: one example of this would be if there was a sudden drop in circulation of a certain type of materials, there is probably something wrong with that section of the library like it’s out of date. But one has to be careful when making assumptions like this: if it’s over a fairly short period of time, it could just be people going on vacation.
However, reference questions and program attendance can be correlated much more strongly to UX. I’ll take a personal example of the Monterey Public Library: we have a program going on here called Stories for Adults. I believe it’s the longest running library story telling program in the country, been going on for at least 20 years now. It’s routinely “sold out”. (In quotes because you can get tickets for free with a library card.) I’ve been to a few of their story telling events, and there’s a reason for the popularity, the story tellers who come to Monterey are quite good.
Reference questions are also an excellent metric for usability. If there’s one question (and I unfortunately don’t have an example here), that’s asked frequently about, for example, finding things in the library, it may be a sign that the library needs to invest in some good wayfinding.
If the library isn’t used much at all, there may be a more serious problem, like a design issue with the building itself. I had this exact problem with the Meriam Library at Chico State, where I received my B.S. I tried using the library a few times but found the layout enough that I basically only used it for the times when I needed tutoring assistance with my classes since, at the time, tutoring was on the fourth floor of the library. Thus, I only used the online resources of the library and for pleasure reading, the city library.
This kind of problem would be non-trivial to fix since even improved wayfinding may not fix the issue because people don’t always read signs. If they have the budget for it, it’d be a great place to renovate to make it easier to navigate, although at Chico State, it was by no means the most confusing building on campus. The volume of use that the Meriam Library receives would make it a worthwhile investment in the future of the campus.