not necessarily
Richard Lynn is the author of the book called
"IQ and the Wealth of Nations"
He uses a clever algorith to take in count of several things and one of them is time leap.
http://www.isteve.com/IQ_table.htm
You can play around with it and notice that the results are not too far off, they are founded and researched and take in consideration time leap. In fact the average IQ of a state does not vary all that much in 4 years.