Statistics vs Underground Economy

Anybody care to comment on the folks, if any there are, who
perhaps are not counted in the government statistics? Might
they not skew the numbers? I am thinking of the newly arrived
in my own Brazilian community (who, I can assure you, would not
be caught dead filling out a census form); and how there might
be folks in other communities such as Chinatown or the
Tenderloin who might be equally invisible? Please excuse if I
undermine the intellectual credibility of the LP by posing
such questions, but I do believe that open, positive, and
*friendly* discussions are most beneficial.