I often see statistics on the number of card holders referenced in library materials. For example, in its recent promotional flyer How Libraries Stack Up: 2010, the OCLC compared the number of public library card holders to the number of credit card holders.
I’m curious to know how this statistic is compiled and what it’s meant to convey. Does it reflect library cards issued or library card users? I ask because my hometown library purges records from its cardholder database every 5 years and a librarian I was speaking with from the midwest said her library does so every 3 years. With such long maintenance windows, these databases obviously contain records of people who have died or moved out of their communities.
Also, having a library card and using it are two very different things. I’d be interested to know how these data points correlate.