The prior probability of a term is defined as the term frequency among all characterized proteins of P. falciparum. In PlasmoDraft it is used both to assess the significance of a TDR, and to measure the specificity of the term. By this way, the ontology root has prior probability equal to 100% and is not at all specific, while the terms closer to the ontology leaves may have very low prior probabilities and be highly specific.
brehelin at lirmm.fr