Growth and Decay Curves in Scientific Citations

In a rapidly advancing scientific discipline, new contributions will supersede older ones. This selection in favor of recent literature should be observable in the distribution of footnote citations in a given discipline, by age of article cited. However, the age distribution of citations also depends on the rate of growth of the disciplinary literature. The effects of growth of the literature and of selection favoring recent articles can be separated, if certain assumptions hold, by use of an exponential model that expands and clarifies earlier findings by Price. This model provides a reasonably good fit to age-distributions of footnotes in several disciplines, and its application suggests that citations in sociology tend to refer to older articles than those in the natural sciences. A parameter in the model, measuring the degree of selectivity in favor of recent articles, can be estimated and may be useful in comparative studies of the communication systems of various disciplines.