Western Europe is a big place. I guess it also depends on whether you only count tests conducted in a professional setting. Here in Germany, i guess at least 20% of people between 20 and 40 have taken some kind of IQ test, e.g. online. Not everyone might admit it because it could come of as a little "vain", but there are even IQ test shows on popular TV channels (Sat 1, RTL 2) where the viewers do the test. They run them at primetime every few years.