The decline in the concentration of citations, 1900-2007

TL;DR

This study analyzes citation patterns from 1900 to 2005 across multiple disciplines, revealing that citation concentration has decreased over time, contradicting previous claims of increasing concentration with online access.

Contribution

It provides a comprehensive, multi-measure analysis of citation dispersion over a century, challenging prior findings about increasing citation concentration.

Findings

Citation dispersion has increased from 1900 to 2005.

All measures show decreasing citation concentration over time.

Contradicts previous research claiming increased concentration with online availability.

Abstract

This paper challenges recent research (Evans, 2008) reporting that the concentration of cited scientific literature increases with the online availability of articles and journals. Using Thomson Reuters' Web of Science, the present paper analyses changes in the concentration of citations received (two- and five-year citation windows) by papers published between 1900 and 2005. Three measures of concentration are used: the percentage of papers that received at least one citation (cited papers); the percentage of papers needed to account for 20, 50 and 80 percent of the citations; and, the Herfindahl-Hirschman index. These measures are used for four broad disciplines: natural sciences and engineering, medical fields, social sciences, and the humanities. All these measures converge and show that, contrary to what was reported by Evans, the dispersion of citations is actually increasing.