Does anyone have reliable statistics (and barring that, reasonable anectdotal evidence) of the fraction of Kohanim, Levi'im, and Yisraelim in various Jewish communities today. By "communities" I don't necessarily mean geographic, but minhagic, like Chabad/Syrian/Litvak, etc.
Answer: Levites: 4%, Priests: 4%.
A scientific article which deals with the genetics of priests and Levites quotes a book from 1999 (not available for reading online) which estimates Levites and priests each at 4% of the general Jewish population. Source: http://www.sciencedirect.com/science/article/pii/S000292970763626X#bbib6 Referenced book: "The genetic origins of Old Testament priests", CE Renfrew, Editor, Population specific polymorphisms, Cambridge University Press, Cambridge, United Kingdom (1999), pp. 31–44
The Persian community (mostly Shirazi) absorbed by Baltimore contains a high fraction of Cohanim and very few Leviim.
Djerba has almost all kohanim.