Price Index (Citation Recency)

The Price Index measures how strongly a field draws on recent literature by computing the percentage of its references that point to work published within the last few years. Derek de Solla Price, the founder of modern scientometrics, observed that the sciences differ sharply in how immediate their referencing is: hard sciences cite a tight cloud of recent papers at the research front, while humanities scholarship cites a long, even spread of older works. In his 1965 Science paper on the networks of scientific papers he documented this concentration of references on recent years, and in his 1970 essay distinguishing hard science, soft science, technology, and nonscience he formalized the index that now bears his name. Defined as the share of references no older than about five years, the Price Index is a citing-side companion to obsolescence measures: where the cited half-life looks at how the literature ages, the Price Index looks at how recency-focused the citing behavior is.