The steady rising of IQ scores over the last century - known as the Flynn effect - causes IQ tests norms to become obsolete over time. To counter this effect, IQ tests are "renormed" (made harder) every 15-20 years by resetting the mean score to 100 to account for the previous gains in IQ scores. But according to new research, such renorming may have unintended consequences, particularly in the area of special education placements for children …showed first 75 words of 735 total…

…showed last 75 words of 735 total…when basing important financial, social or legal decision on IQ scores," say the researchers. "Perhaps the most important times to be particularly cautious are when a test is either at the beginning or at the tail end of its norming cycle. Although test scores are most valid at the beginning of a norming cycle, they run the greatest risk of being compared to highly inflated scores from the waning years of the previous norming cycle."