A model showing the increase in time of the average and median reference age and the decrease in time of the Price Index

This paper proves two regularities that where found in the paper (Larivière et al. (2007). Long-term patterns in the aging of the scientific literature, 1900–2004. In Proceedings of ISSI 2007. CSIC, Madrid, Spain, pp. 449–456.). The first is that the mean as well as the median reference age increases in time. The second is that the Price Index decreases in time. Using an exponential literature growth model we prove both regularities. Hence we show that the two results do not have a special informetric reason but that they are just a mathematical consequence of a widely accepted simple literature growth model.