Self-consistency test of the algorithm. Fraction of references from the stem cell training set (F) retrieved when selecting a number (N) of top-scoring references in a mixed set combining the training set and the random set. Nouns are better discriminators with F = 0.87 for the top half of the list. F was 0.79 for adjectives, 0.73 for verbs, and 0.70 for nouns plus adjectives. Performance could not be theoretically perfect because there were articles in the training set which were not relevant to stem cells, and there were articles in the random set which were relevant to stem cells.