The Bibliometric Properties of Article Readership Information

Digital libraries such as the NASA Astrophysics Data System (Kurtz et al., 2005) permit the easy accumulation of a new type of bibliometric measure, the number of electronic accesses (“reads”) of individual articles. We explore various aspects of this new measure. We examine the obsolescence function as measured by actual reads and show that it can be well fit by the sum off our exponentials with very different time constants.We compare the obsolescence function as measured by readership with the obsolescence function as measured by citations. We find that the citation function is proportional to the sum oftwo ofthe components ofthe readership function. This proves that the normative theory of citation is true in the mean. We further examine in detail the similarities and differences among the citation rate, the readership rate, and the total citations for individual articles, and discuss some ofthe causes. Using the number ofreads as a bibliometric measure for individuals, we introduce the read–cite diagram to provide a two-dimensional view ofan individual’s scientific productivity. We develop a simple model to account for an individual’s reads and cites and use it to show that the position ofa person in the read–cite diagram is a function of age, innate productivity, and work history. We show the age biases ofboth reads and cites and develop two new bibliometric measures which have substantially less age bias than citations: SumProd, a weighted sum oftotal citations and the readership rate, intended to show the total productivity ofan individual; and Read10, the readership rate for articles published in the last 10 years, intended to show an individual’s current productivity. We also discuss the effect of normalization (dividing by the number ofauthors on a paper) on these statistics. We apply SumProd and Read10 using new, nonparametric techniques to compare the quality of different astronomical research organizations.