Figure 4. Referencing behavior for authors of different academic age (number of years spent in the field) in five disciplines (astronomy (AST), mathematics (MAT), robotics (ROB), ecology (ECL), and economics (ECN)).

A) Number of references per page (reference rate). B) Average age of references. C) Modified Price Index (fraction of references published within five years compared to those published within 10 years). D) Re-citation fraction (repeated citations in pairs of articles). Authors who appear once have x = 1. First two years not binned; afterwards data are averaged in bins of four. Bins with fewer than 4 authors (rightmost, see Figure 1A) are excluded. For re-citation (D) points are not shown for the first two years because the average span between the pair of publications is less than it is for later ages.