Figure 10.10: Average scores on four mental tests as a function of age The scores on each test are normalized (by the method described in the Appendix at the back of this book) such that 0 is the average for all subjects combined. A score of +1 or more would place a person in the top 84 percent of all subjects tested, and a score of −1 or less would place one in the bottom 16 percent.
(Based on data from Salthouse, 2004.)