The number of distinct tags assigned per PubMed citation by the aggregate of Connotea users. The figure provides a probability density histogram of the number of distinct tags per PubMed citation within Connotea. For each citation, the non-redundant set of tags assigned to that citation by all of the users to post it to their collections is counted. The peak of the distribution (just under a density of 0.3) is at one tag per citation (all Connotea posts have at least one tag) and it drops off smoothly as the number of tags per citation increases down to negligible number beyond about 11 tags per document.
Good et al. BMC Bioinformatics 2009 10:313 doi:10.1186/1471-2105-10-313