Following publication, Alf Eaton (http://hublog.hubmed.org) re-implemented the analysis in this paper, using PHP code. This was then used to independently generate and verify Figure 1 (https://docs.google.com/spreadsheet/pub?key=0AjePz4Y_bB3hdFJGZ0M2VGx3N2tlX3pIemhUSTZlbkE&gid=5).

For anyone looking to conduct similar quantitative literature analyses, his code was more concise than ours and may be more convenient for those who are not familiar with the R language and statistical environment.