Use Studies and the NDP
The Normative Data Project (NDP) is currently designed to measure aspects of the use of public libraries in the US and Canada. It can report on the collections and circulations both in narrow time frames, but also will be capable of following the use of materials through time as the database grows.
There is an extensive literature both on collection evaluation and on how people use libraries – in fact, there is even a secondary literature that reviews these use studies and synthesizes results. These studies will be examined in the months ahead to see what hints they can give us – not only about what kinds of values to expect for NDP variables as a part of the vetting process, but also to see what analysts have thought important to measure when trying to find out what people use in a library. In fact, the reports on the default NDP Dashboard were suggested by these studies.
What does a first look at this literature tell us about library use? Robert Broadus succinctly summarized results of a number of studies in 1980 and said: "The most important general conclusions reached so far through use studies of library materials are judged to be: (1) recorded use in many libraries is low; (2) use within the library parallels circulation; (3) past use predicts future use; (4) recent materials are used more frequently; and (5) Americans use few foreign-language materials."
Two sample reports available on this Web site concur with the conclusion about foreign language materials, because they show English language materials account for almost 99% of the materials held in the NDP libraries and in items circulated. Even though it has been 25 years since those conclusions were published, they are still true.
There has been a methodological difficulty with these studies, though.
Studies have focused on use at a narrow period of time and from analysis of that narrow period, inferred characteristics about the behavior of circulation and library use through time. Line and Sandison rigorously pointed out difficulties with this approach and cast doubt on the notion of "obsolescence" – that is, that the measured decline in use of materials over time – a consistently repeated observation – is the result of materials becoming obsolete. They demonstrated that changes in use over time could well be a result of the amount of materials published which increased over time. However, numerous studies have demonstrated the effect of time on collections: older materials, generally, circulate less.
Fussler and Simon were concerned with putting materials in storage – theirs was a study of academic libraries where storage of little-used materials is often necessary. Predicting what will not circulate is a part of the consideration of what goes in to storage and what does not, and it is a difficult thing to do when you are looking at use of materials over a few days. For some questions, the best data to look at are data generated over long periods of time.
This question of storage of materials may not seem to be a matter of concern to the NDP and public libraries. But if you can predict what will not be used, you must be able to predict what will be used and this question is important to public libraries and to the NDP. We know from use studies that past use of materials is a predictor of future use, but what about new books? How does the population demographics of a library's market area affect use of materials? If we can address these questions, then we can build collections that will be used, and spend money more wisely.
However, actually measuring the behavior of a set of books through time is extraordinarily difficult, let alone predicting future use. In rereading these early studies, the difficulties faced and the clarity of thought required in addressing them seems considerable.
It was only recently, however, that computers had the capacity to hold sufficient data to allow such analysis. The NDP is designed to permit longitudinal studies, among others, to allow us to follow trends in use through time. Making this kind of study possible is a complex undertaking.