“The Range of Human Capacities”, 1935 (; backlinks; similar):
Edward Thorndike saw that the subjects who did well at the start of the training also improved faster as the training progressed compared with the subjects who began more slowly. “As a matter of fact”, Thorndike wrote, “in this experiment the larger individual differences increase with equal training, showing a positive correlation with high initial ability with ability to profit by training.” The passage from the Bible doesn’t quite capture Thorndike’s results accurately because every subject improved, but the rich got relatively richer. Everyone learned, but the learning rates were consistently different.
When World War I erupted, Thorndike became a member of the Committee on Classification of Personnel, a group of psychologists commissioned by the US Army to evaluate recruits [see 1918]. It was there that Thorndike rubbed off on a young man named David Wechsler, who had just finished his master’s degree in psychology. Wechsler, who would become a famous psychologist, developed a lifelong fascination with tracing the boundaries of humanity, from lower to upper limits.
In 1935, Wechsler compiled essentially all of the credible data in the world he could find on human measurements. He scoured measures of everything from vertical jump to the duration of pregnancies to the weight of the human liver and the speeds at which card punchers at a factory could punch their cards. He organized it all in the first edition of a book with the aptly momentous title The Range of Human Capacities.
Wechsler found that the ratio of the smallest to biggest, or best to worst, in just about any measure of humanity, from high jumping to hosiery looping [knitting], was between 2 to one and 3 to one. To Wechsler, the ratio appeared so consistent that he suggested it as a kind of universal rule of thumb.
Phillip Ackerman, a Georgia Tech psychologist and skill acquisition expert, is a sort of modern-day Wechsler, having combed the world’s skill-acquisition studies in an effort to determine whether practice makes equal, and his conclusion is that it depends on the task. In simple tasks, practice brings people closer together, but in complex ones, it often pulls them apart. Ackerman has designed computer simulations used to test air traffic controllers, and he says that people converge on a similar skill level with practice on the easy tasks—like clicking buttons to get planes to take off in order—but for the more complex simulations that are used for real-life controllers, “the individual differences go up”, he says, not down, with practice. In other words, there’s a Matthew effect on skill acquisition.
Even among simple motor skills, where practice decreases individual differences, it never drowns them entirely. “It’s true that doing more practice helps”, Ackerman says, “but there’s not a single study where variability between subjects disappears entirely.”
“If you go to the grocery store”, he continues, “you can look at the checkout clerk, who is using mostly perceptual motor skill. On average, the people who’ve been doing it for 10 years will get through 10 customers in the time the new people get across one. But the fastest person with 10 years’ experience will still be about 3× faster than the slowest person with 10 years’ experience.”
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