IQ Yo-Yo: Test changes alter retardation diagnoses

Since average scores on particular IQ tests rise a few points every 3 or 4 years, those tests become obsolete after a couple of decades. In order to reset the average score to 100, harder IQ tests are devised every 15 to 20 years.

Trickier tests have no practical impact on people who score within the normal IQ range of 90 to 110.