Determining the publication impact of a digital library

We attempt to assess the publication impact of a digital library (DL) of aerospace scientific and technical information (STI). The Langley Technical Report Server (LTRS) is a digital library of over 1,400 electronic publications authored by NASA Langley Research Center personnel or contractors and has been available in its current World Wide Web (WWW) form since 1994. In this article, we examine calendar year 1997 usage statistics of LTRS and the Center for AeroSpace Information (CASI), a facility that archives and distributes hard copies of NASA and aerospace information. We also perform a citation analysis on some of the top publications distributed by LTRS. We find that although LTRS distributes over 71,000 copies of publications (compared with an estimated 24,000 copies from CASI), citation analysis indicates that LTRS has almost no measurable publication impact. We discuss the caveats of our investigation, speculate on possible different models of usage facilitated by DLs, and suggest “retrieval analysis” as a complementary metric to citation analysis. While our investigation failes to establish a relationship between LTRS and increased citations and raises at least as many questions as it answers, we hope it will serve as an invitation to, and guide for, further research in the use of DLs.