Lexicostatistics is an approach to comparative linguistics that involves quantative comparison of cognates. It is to be distinguished from glottochronology, which attempts to use lexicostatistical methods to estimate the length of time since two or more languages diverged from a common earlier proto-language. This is merely one application of lexicostatistics, however, and other applications of it may not share the assumption of a constant rate of change for basic lexical items.