I went to hear Greg Clark give a noontime seminar at Cato today. He is fairly persuasive in person. One thing about pursuing a line of thought for a long time when most people disagree with you is that your arguments tend to get pretty sharp.
During the discussion afterward, somebody brought up the Stanford Marshmallow Experiment. You can Google that subject to find out much more, but here is one site that mentions it.
In one of the most amazing developmental studies ever conducted, Walter Michel of Stanford created a simple test of the ability of four year old children to control impulses and delay gratification. Children were taken one at a time into a room with a one-way mirror. They were shown a marshmallow. The experimenter told them he had to leave and that they could have the marshmallow right then, but if they waited for the experimenter to return from an errand, they could have two marshmallows. One marshmallow was left on a table in front of them. Some children grabbed the available marshmallow within seconds of the experimenter leaving. Others waited up to twenty minutes for the experimenter to return. In a follow-up study (Shoda, Mischel, & Peake, 1990), children were tested at 18 years of age and comparisons were made between the third of the children who grabbed the marshmallow (the "impulsive") and the third who delayed gratification in order to receive the enhanced reward ("impulse controlled").
The third of the children who were most impulsive at four years of age scored an average of 524 verbal and 528 math. The impulse controlled students who scored 610 verbal and 652 math! This astounding 210 point total score difference on the SAT was predicted on the basis of a single observation at four years of age! The 210 point difference is as large as the average differences between that of economically advantaged versus disadvantaged children and is larger than the difference between children from families with graduate degrees versus children whose parents did not finish high school! At four years of age gobbling a marshmallow now v. waiting for two later is twice as good a predictor of later SAT scores than is IQ.
The quoted source sees the Marshmallow experiment as showing the importance of emotional intelligence. The economists at the Clark seminar just thought of it as a remarkably reliable indicator of general intelligence--apparently even better than IQ. Also, the economists see this as a measure of time preference, rather than impulse control. That may be more than a mere matter of terminology.
Clark's view of the world is that differences in average individual characteristics, such as time preference, account for a lot of differences in the standard of living, even holding things like institutions constant. He acknowledges that places like North Korea and Zimbabwe are poster children for the role of institutions, but he warns us not to get caught up in confirmation bias. There are, he argues, also quite a few poster children for countries where institutions appear to be decent, but poverty is still severe.
Anyway, if you, like me, were unaware of what clearly must be a classic in empirical psychology, consider yourself enlightened.