Oh, I'm sure we can estimate this. Let's see, judging by the ToC, I'd estimate that the current issue of Nature has about 100 authors. Taking this back 10 years gives us about 12,000 authors. This is assuming that none of these authors published more than once which is hilghly unlikely. That would give us around 1200 authors who have contributed to the Wiki. Judging by this, it would seem that 10% is a valid estimation of how many experts vs. laymen have contributed to the Wiki.
So it's safe to assume that we can't use the same number of authors for every journal since many won't be unique authors. Would you agree with this?
You have a valid point. So what do you think would be a fair number? It would seem that you are in a catch-22. Either the number of experts contributing is low, thus the number of errors in the Wiki is high, or there are a high percentage of experts contributing to the Wiki and yet the number of errors is still high. If the latter is true, then it shows that either the experts are publishing errors, ignoring errors, or do not have enough influence.
Nature has German, Chinese, Japanese, and Korean versions. How many of those authors do you think only speak English?