The 15,000th author registered recently on the RePEc Author Service (which also has another 5,000 registered, but without any works in their profile). See a list of all those registered at EconPapers or IDEAS. This give us the opportunity to reflect on the coverage of this service: what proportion of academic economists is covered? Let me offer a few suggestions.
Assume that the works listed in RePEc provide a representative sample of all the works written by economists. Then determine how many of these works are listed in the profile of a registered author. By that account, about 40.1% have been claimed, and thus about 40% of the profession would be registered with RePEc. This latter number is in reality higher, due to several biases: a) some authors are not alive and cannot register; b) some registered authors have the unfortunate habit to remove from their profile working papers once they are published; c) some works listed are not written by economists, and these authors are less likely to register with RePEc.
Alternatively, estimate the number of authors in the world from the membership in academic societies. I guess the three largest societies are the American Economic Association (18,000 members), the European Economic Association (2,300 members) and the Econometric Society (5,500 members). Obviously, their membership overlaps, and not every of their members is an author. But not every economist is member either. Assume that adding their membership numbers corrects for all mismeasurements, then the RePEc Author Service covers 58% of the profession.
One can also observe a specific subsample of economists, those listed among the top 1000 by Tom Coupé. There, the RePEc Author Service covers 75% of the top 1000 by publications and 65% of the top 1000 by citations (which includes quite a few non-economists). But we have good reasons to believe these proportions are higher than for the whole population. Indeed the proportion is significantly higher for the better ranked within this sample, and we can extrapolate that those outside the top 1000 are less represented in the RePEc Author Service.
In summary, the RePEc Author Service covers between 40% and 75% of the profession. Possibly less, possibly more, likely in between.