Precision increase and coverage decrease with voting in CiteULike. The X axis indicates the minimum number of times a given UMLS Concept would need to be associated with a PubMed citation (through the assignment of a tag by a CiteULike user that could be linked to the Concept) to be considered. If no concepts can be identified for a particular document at each threshold, the document is removed from consideration. The Y axis shows the fraction of PubMed citations associated with UMLS Concepts at each threshold. Only Concepts are plotted as each Concept is linked to a Semantic Type and a Semantic Group hence the other plots would be redundant.