IQ & Income
In 1900, the vast majority of very bright young adults did not get a college education, and even by the mid-1920s only about half of those in the top IQ decile were entering college. By the 1960s, the probability that those in the top IQ decile would enter college was almost 100%, regardless of whether they were rich or poor, white or black.
The mean SAT score for entering freshmen at Harvard rose so dramatically that the average freshman in 1952 would have been in the bottom 10% of the class in 1960.
In constant dollars, an engineer earned about $30,000 in 1952 compared with $20,000 for a manufacturing worker, which was not much different from the ratio at the beginning of the century. By 1988, the engineer earned almost $75,000 compared with $22,000 for the manufacturing worker.
The NLSY (National Longitudinal Survey of Youth) contains a sample of almost 13,000 young people who have been interviewed periodically from 1978 on. By 1992, the subjects were 28 to 35 years old. The data on siblings applied to nearly 3,000 sibling pairs who had the same biological parents, lived with their biological parents at least through the younger sibling’s 7th year, and had valid scores on the Armed Forces Qualification test. Where the IQ differed, the results were striking. For example, where both children had attended elementary and secondary schools for the same number of years, only 18% of the siblings with “normal” IQs (in the 90 to 109 range) got bachelor’s degrees, while 83% of their brothers or sisters in the very bright category (IQ of 125 or above) did so.
A measure called the Duncan scale, which runs from 1 to 100, ranks occupations according to pay, prestige, educational requirements, and similar factors. For the siblings with normal IQs, the median Duncan score was 41. For the brightest brothers and sisters it was 62 — indicating managerial, administrative, and professional positions — and for the dullest it was 11.
Median income was $19,000 for the middle IQ range, for the brightest it was $30,000, and for the dullest it was $7,500. Particularly for those in the brighter groups, incomes can be expected to increase as they get older, while those in occupations lower in the Duncan scale cannot expect such increases later in life.