There are more than 100 vocabulary sets defined internationally for some purpose. Only two independent, reasonably recent, comparative studies in the clinical domain have been found. This study compared these systems across a range of clinical terminological tests involving diagnoses, findings, modifiers, treatments and procedures and others . No system covered all the concepts. The authors noted how poorly the ICD systems capture the content of clinical work.
Clarity is important from an information retrieval perspective.
UMLS was the only system with definitions but did not otherwise fare as well as the other two systems. It should be noted that this study used a very early Clinical Terms Version 3 release when much of the project work remained to be incorporated. Clinical Terms Version 3 have complementary strengths and weaknesses. For the future there is much to be gained by combining these two standards and the current discussions between the two organisations have the potential to produce the world leader in standard clinical vocabularies. However at the moment the possibilities and time scales remain uncertain to this committee.