'Tis true in other walks of life, too.

In surveys in the UK, if you ask in the street about what newspapers people buy, apparently 40% buy broadsheets and 10% The Sun. Sales are about the other way around!

The UK TV viewer preference surveys have struggled for years to get an accurate picture (pun not intended) becuase so many people will tell you they watch worthy TV when they really watch soaps - some have even ben found to wtch the worthy stuff for a couple of weeks because there is a set-top box recording what they watch...