Formal Properties of the Metathesaurus: An Update*.

The formality of the Metathesaurus stems from the way that its concepts are related to one another. Thus our first interest is in the relative stability of those concepts. In 1994, we observed that atoms, names in a constituent terminology, are being added to the Metathesaurus faster than concepts, unique, named meanings. Figure 1 shows the number of atoms and concepts in the reviewed portion of the six versions of the Metathesaurus, and the 1995 Metathesaurus continues the trend toward convergence. If this continues for future versions of the Metathesaurus, it may indicate the emergence of an empirical consensus on the identity of biomedical concepts independent of what they are called.