6. Intrigued by these results, the researchers, then graduate students at Harvard University, decided that they needed to explore a different source of data, in case some aspect of collecting data on the Internet was skewing the results. They dug out sets of data, collected decades ago, on adult performance at different ages on the Wechsler Adult Intelligence Scale, which is used to measure IQ, and the Wechsler Memory Scale. Together, these tests measure about 30 different subsets of intelligence, such as digit memorization, visual search, and assembling puzzles.
Hartshorne and Germine developed a new way to analyze the data that allowed them to compare the age peaks for each task. “We were mapping when these cognitive abilities were peaking, and we saw there was no single peak for all abilities. The peaks were all over the place,” Hartshorne says. “This was the smoking gun.”