The graphs in Fig. 2 trace the influence of online access, estimated from the entire sample of articles, and illustrated for journals and subfields with the mean number of citations. Figure 2A shows the simultaneous effect of commercial and free online availability on the average age of citations

The first question was whether depth of citation—years between articles and the work they reference—is predicted by the depth of journal issues online—how many years back issues were electronically available during the previous year when scientists presumably drafted them into their papers.

Collectively, the models presented illustrate that as journal archives came online, either through commercial vendors or freely, citation patterns shifted. As deeper backfiles became available, more recent articles were referenced; as more articles became available, fewer were cited and citations became more concentrated within fewer articles. These changes likely mean that the shift from browsing in print to searching online facilitates avoidance of older and less relevant literature. Moreover, hyperlinking through an online archive puts experts in touch with consensus about what is the most important prior work—what work is broadly discussed and referenced. With both strategies, experts online bypass many of the marginally related articles that print researchers skim. If online researchers can more easily find prevailing opinion, they are more likely to follow it, leading to more citations referencing fewer articles. Research on the extreme inequality of Internet hyperlinks (14), scientific citations (15, 16), and other forms of “preferential attachment” (17, 18) suggests that near-random differences in quality amplify when agents become aware of each other’s choices. Agents view others’ choices as relevant information—a signal of quality—and factor them into their own reading and citation selections. By enabling scientists to quickly reach and converge with prevailing opinion, electronic journals hasten scientific consensus. But haste may cost more than the subscription to an online archive: Findings and ideas that do not become consensus quickly will be forgotten quickly .

This research ironically intimates that one of the chief values of print library research is poor indexing. Poor indexing—indexing by titles and authors, primarily within core journals— likely had unintended consequences that assisted the integration of science and scholarship. By drawing researchers through unrelated articles, print browsing and perusal may have facilitated broader comparisons and led researchers into the past. Modern graduate education parallels this shift in publication—shorter in years, more specialized in scope, culminating less frequently in a true dissertation than an album of articles (19)

As 21st-century scientists and scholars use online searching and hyperlinking to frame and publish their arguments more efficiently, they weave them into a more focused—and more narrow—past and present.