It's important to note that IQ test scores have only ordinal properties--one cannot make interval inferences from them validly, for example the frequently heard assertion that "A child with an IQ of 150 is as different in intelligence from a normal child as a child with an IQ of 50." Such a statement is very hard to verify in the first place, but in any event IQ scores show ORDINAL relationships (subject to a lot of error of estimation) but don't show interval relationships of how far (on the same scale) one score is from another in any valid way.
