OBSOLESCENCE OF THE PATENT LITERATURE

Abstract

Patents deserve bibliometric study both for their own sake and because their formality can be exploited. Here the year by year issue of US patents since 1836 is used to correct for growth their apparent aging, as obtained by a synchronous study of citations made by (a) US patent examiners and (b) periodicals. Apparent and corrected aging are treated in terms of conditional probabilities. In (a), whereas the recent apparent aging of chemical patents is much faster than that of the whole, after correction the rates are very close. Using a very broad (trichotomous) subject classification, no cut‐off dates for novelty searches can be established if total recall is the goal. The strictly retrospective method of such searches is invoked to explain why a linearity found here in one type of corrected aging function has also been found for a search file truncated at 1920. In (b) the now classic exponential form of aging applies back to the twenties, but older patents are cited too frequently to conform. The deviation is graphically even more striking after correction for growth and is probably due to citations made for historical purposes.