Frequency distribution of IQ scores in a population with a mean of 100 and a SD of 15. Note that 2.5% of the scores lie below 71 (the Florida cut-off), 5.1% are below 76 (the Hall Court’s suggestion), and 16.7% are below 86 (an older cut-off) (IQ scores are integers, and the height of each bar is proportional to the relative number of people at each integer. The normal curve is a continuous line that fits these heights. In this figure and throughout this article, I use the area under the curve from x – 0.5 to x + 0.5 to compute the proportion of people with an integral IQ score x.).