How many English words are of native origin?

What percentage of current English words are of native Anglo-Saxon origin? I have seen stats about how large percentages of the English words currently in use come from French, Latin, or German origins, but I want to know how many truly native words the English language has left.

I can't find a duplicate.

This Wikipedia article gives:

Estimates of native words (derived from Old English) range from 20%–33%, with the rest made up of outside borrowings.

References are given at the end of the article, but it is not mentioned which ones contain surveys arriving at these estimates.