Will Europe Knock the U.S Out of the #1 Spot? Key to Warren Buffett’s Early Success

Efficient Markets and the Countries that Have Them

We've found over the years that European markets are much less efficient than those in the U.S. Right now we have less than 5% of our portfolio in the U.S., and it's really lower because our largest holding that trades there operates in the U.K.
Source: http://www.valueinvestorinsight.com/