Usage Impact
is correlated with Citation Impact
(Physics ArXiv: hep, astro, cond, quantum; math, comp)
http://citebase.eprints.org/analysis/correlation.php


(Quartiles Q1 (lo) - Q4 (hi))
All         r=.27, n=219328
Q1 (lo)    r=.26, n=54832
Q2          r=.18, n=54832
Q3          r=.28, n=54832
Q4 (hi)    r=.34, n=54832


hep      r=.33, n=74020
Q1 (lo)   r=.23, n=18505
Q2         r=.23, n=18505
Q3         r=.30, n=18505
Q4 (hi)   r=.50, n=18505

(correlation is highest for high-citation papers/authors)
Most papers are not cited at all
Average UK downloads per paper: 10
(UK site only: 18 mirror sites in all)