Have linguists measured the rate of evolution of a language by analyzing the rate of change of the language's words' usages over time? Is there a term for this sort of measurement?
For example, suppose a language has N words (or usages of a word) W0, W1, W1, …, Wn. For each Wi one could associate a rate of increase or decrease Ri (e.g., determined with Google's N-grams or, better, using some other smarter means which can distinguish usages). Then the rate of change of the language could be estimated by taken some kind of average of all the Wi.