How much space does a library need? Justifying collections space in an electronic age

In 2002, plans to merge Penn State's Physical Sciences Library and Mathematics Library provoked a controversy in the Eberly College of Science over the size of the library needed to support its departments. The College contended that a physical collection no more than 5 years old was adequate. A study of astronomy, chemistry, mathematics, physics, and statistics faculty publications showed that a much older collection was required to include 90% of their cited references. How much older varied by discipline. These data were then used to determine collection space allocations in the new library. A follow-up study in 2007 found that the patterns were generally still valid. Although the results are specific to Penn State, the data may be similar to other U.S. institutions with similar degree programs. The method is easily adaptable to other institutions.