Thomas also presents a simple equation for deriving an index of persistence, which weights not only the number of stems ('roots') per meaning, but their relative frequency. Thus his persistence values for some stem frequencies per meaning is: stem identical in 8 languages, 100%; stem frequencies 7 and 1, 86%; stem frequencies 4 and 4, 64%; stem frequencies 4, 3, and 1, 57%. His formula will have to be weighed, may be altered or improved, and it should be tested on additional bodies of material. But consideration of the frequency of stems per constant meaning seems to be established as having significance in comparative situations with diachronic and classificatory relevance; and Gleason presumably is on the way with a further contribution in this area.

As to relative frequencies of competing roots (7 -- 1 vs. 4 -- 4, etc.), Thomas with his 'weighting' seems to be the first to have considered the significance this might have. The problem needs further exploration. I was at least conscious of the distinction in my full Yokuts presentation that awaits publication, in which, in listing 'Two Stem Meanings', I set off by asterisks those forms in which n of stem B was ** f of stem A 3, the unasterisked ones standing for ** f; or under 'Four Stems', I set off by asterisks cases where the combined n of stems ** f was ** f.

These findings, and others which will in time be developed, will affect the method of glottochronological inquiry. If adjectival meanings show relatively low retentiveness of stems, as I am confident will prove to be the case in most languages of the world, why should our basic lists include 15 per cent of these unstable forms, but only 8 per cent of animals and plants which replace much more slowly? Had Hoijer substituted for his 15 adjectival slots 15 good animal and plant items, his rate of stem replacement would have been lower and the age of Athabascan language separation smaller. And irrespective of the outcome in centuries elapsed since splitting, calculations obviously carry more concordant and comparable meaning if they deal with the most stable units than with variously unstable ones.