Quantitative or numerical metrics of protein function specificity made possible by the Gene Ontology are useful in that they enable development of distance or similarity measures between protein functions. Here we describe how to calculate four measures of function specificity for GO terms: 1) number of ancestor terms; 2) number of offspring terms; 3) proportion of terms; and 4) Information Content (IC). We discuss the relationship between the metrics and the strengths and weaknesses of each.
Louie, B., Bergen, S., Higdon, R., & Kolker, E. (2010). Quantifying protein function specificity in the gene ontology. Standards in Genomic Sciences, 2(2), 238–244. https://doi.org/10.4056/sigs.561626