Figure 2. Trends involving numbers of references for 5 disciplines (astronomy (AST), mathematics (MAT), robotics (ROB), ecology (ECL), and economics (ECN)) from 1961–2010.

A) The number of references per article. B) The article length, i.e. number of pages per article. C) Number of references per page (reference rate). Data for ROB start in 1983. Page information is missing for some articles in the late 1960s. Data points are averaged in bins of 2 years.