Česky
Slovensky
EnglishTwo men who failed to make the cut for a study of gifted children later won the Nobel Prize in Physics. William Shockley, co-inventor of the transistor, and Luis Alvarez, one of the most influential experimental physicists of the twentieth century, were both tested in the 1920s for Lewis Terman's famous study of young geniuses. Neither reached the IQ cutoff of 135 that Terman had drawn, so neither one got in.
Here is the other half of the story. Of the nearly 1,500 children who did make it into Terman's study, not a single one went on to win a Nobel or a Pulitzer across an entire lifetime.
So does IQ predict success? The honest answer isn't yes or no; it's a matter of degree. And the longitudinal studies that follow the same people for decades give us surprisingly concrete numbers to hang on that degree.
The Termites: a study that has run for a century
In 1921, Stanford psychologist Lewis Terman launched one of the most ambitious research projects in the history of the field. He selected 1,528 California children with an IQ of 135 or higher, roughly the top 1% of the population, and set out to track them for the rest of their lives. The participants were nicknamed the Termites. The study is still running today, having outlived its founder to become the longest longitudinal project of its kind.
Terman wanted to debunk a popular belief of his era: that clever children were frail, sickly, and socially awkward. He managed it. On average, the Termites turned out healthier, better educated, more professionally accomplished, and more satisfied than the general population. High IQ demonstrably helped them in life.
But Terman was after something bigger. He wanted to prove that his children would become the intellectual elite of the nation, and there he hit a wall. The Termites grew into successful doctors, lawyers, professors, and engineers, yet none of them reshaped their field. Meanwhile, two boys his test had turned away walked off with Nobel Prizes.
The study has its critics. The sample was not random. Teachers nominated the children and Terman hand-picked some himself, so influences other than raw IQ could have crept in, whether class popularity or a comfortable family background. It remains unique all the same, since no one else has followed such a large group of gifted people for so long.
What should you take from this? A high IQ nudges the probability of success upward, but on its own it is not enough for greatness. Past a certain point, other things start to decide the outcome, and we will get to those.
Inside the top 1%, there is no ceiling
Terman's cutoff of 135 carried a hidden assumption. It quietly took for granted that above that line everyone was roughly equal, that the gap between an IQ of 135 and an IQ of 165 made no difference to results. Newer research showed that this simply is not true.
The Study of Mathematically Precocious Youth, or SMPY, was founded in 1971 by Julian Stanley at Johns Hopkins University. It is now led by David Lubinski and Camilla Benbow at Vanderbilt University. The project identifies children by their scores on the SAT, taken before the age of 13, and follows them for decades. It has tracked more than 5,000 exceptionally able people.
Lubinski and Benbow did something that had never occurred to Terman: they split the top 1% into quartiles by ability. It turned out that even inside this narrow elite, more really is better. The top quarter of the top percent beat the bottom quarter on nearly everything, from doctorates and patents to peer-reviewed publications and income.
Take one example. The odds of earning tenure at one of the 50 best American universities ran around 3.2% for people in the top quartile, against just 0.38% for the bottom quartile. That is roughly an eightfold difference, and every one of these people already belonged to the top 1% of the population. No threshold beyond which IQ stopped mattering ever showed up in the data.
What the meta-analyses say
Longitudinal studies follow one specific group of people. Meta-analyses run in the opposite direction, pooling dozens of independent studies to work out how strong the link between IQ and life outcomes is across tens of thousands of people.
In 2007, the Estonian sociologist Tarmo Strenze summarized the longitudinal studies in which IQ was measured in childhood and success only in adulthood. The correlation between intelligence and educational attainment came out around .56, and with occupational prestige around .43. For income the link was weaker, roughly .2. Put differently, IQ is tied most tightly to education, more loosely to the prestige of the job, and more loosely still to the paycheck itself.
Better known still is the work of Frank Schmidt and John Hunter from 1998, which drew together 85 years of hiring research. Their conclusion: general mental ability is the single best predictor of job performance that recruiters have. Across all occupations the correlation came out around .51, and for complex managerial and professional roles higher still, near .58. Years of experience and level of education did not come anywhere close.
| Study (author, year) | What it tracked | Scope | Main finding |
|---|---|---|---|
| Terman (from 1921) | Children with IQ 135+ across their whole lives | 1,528 people, over 80 years | The gifted prosper, yet none won a Nobel or a Pulitzer |
| SMPY (from 1971) | Exceptionally able youth (SAT before 13) | 5,000+ people, over 50 years | Even in the top 1%, more is better; no ability ceiling |
| Strenze (2007) | Meta-analysis of IQ vs. socioeconomic success | Dozens of studies, tens of thousands of people | Education r≈.56, occupation r≈.43, income r≈.2 |
| Schmidt & Hunter (1998) | Meta-analysis of predictors of job performance | 85 years of hiring research | Cognitive ability is the best single predictor, r≈.51 |
What do those numbers actually mean? A correlation around .5 counts as moderate to strong in psychology. In practice it says that IQ explains roughly a quarter of the differences between people on a given outcome. For a single factor that is a lot, and at the same time it leaves three quarters to everything else.
One more caveat belongs here. A correlation on its own says nothing about cause and effect. A higher IQ probably helps you get more education, but the reverse holds too, because staying in school longer nudges measured IQ up a little. In real life the link between ability and success runs in both directions.
Why IQ predicts performance
Why would a single general ability predict things as varied as school grades and job performance? The most common explanation is a simple one. Higher cognitive ability means faster learning and better handling of complexity. Anyone who grasps new material quickly and spots the connections in it gains an edge in any profession where something new keeps turning up.
That is exactly why the validity of IQ climbs with the complexity of the work. In routine jobs, where tasks repeat, intelligence plays a smaller part. For a doctor, a programmer, or an analyst running into fresh problems every day, it shows up in full. The Schmidt and Hunter data make the pattern plain: the more demanding the role, the more strongly cognitive ability predicts the outcome.
Picture two new colleagues in the same junior role. The one with higher cognitive ability picks up the company systems faster. She starts delivering value sooner, so she gets handed tougher assignments. Within a few years a small head start in learning has turned into a big head start in a career, because the effect keeps compounding.
What IQ doesn't predict
Those remaining three quarters are not random noise. Behind them sit factors that have no direct link to intelligence, and some of them predict success almost as well as IQ does.
Conscientiousness, one of the five dimensions of personality in the Big Five model, repeatedly turns up as a strong predictor of job performance and income, independent of IQ. Someone who is reliable, organized, and finishes what they start will routinely overtake a smarter colleague coasting on talent alone. In 2007 Angela Duckworth described a related trait, grit, meaning perseverance and passion for long-term goals.
Socioeconomic background carries real weight too. Strenze's meta-analysis confirmed that family origin correlates with later income and status about as strongly as IQ does. The child of educated, well-off parents gets better schools, better contacts, and a safety net for when things go wrong. Then there is luck: the right timing, a chance meeting, the state of the job market at the moment you step into it.
And then comes satisfaction with life, where IQ nearly gives up altogether. The link between intelligence and how content a person feels with their own life is very weak, close to zero. Smarter people are not happier on average; they tend to have different worries instead. The money and prestige that track with IQ do not guarantee happiness by themselves.
How much of your own wins and losses do you think falls into that "everything else" category? For most people it turns out to be more than they would guess.
Correlation is not destiny
This is where almost everyone reading studies like these makes the same mistake. A correlation of .5 holds for large groups, not for you as an individual. The statistics say that people with higher IQs earn more on average. They do not say whether one particular person with an IQ of 128 out-earns the neighbor with an IQ of 108.
Take two graduates of the same program, one with an IQ of 130 and one with 110. If we had to bet on which of them reaches a higher position in twenty years, statistically we would put our money on the first. But if we placed that bet on a thousand similar pairs, we would be wrong for a large share of them, because personality, health, family, chance, and hundreds of other influences shaped the results too.
IQ works more like a tailwind than a set of rails. It raises the probability, opens doors, and makes learning easier. The direction you choose, and whether you stick with it, stays largely up to you. If you are curious where you sit on that scale and which kinds of reasoning you are strongest in, you can take an IQ test and treat the result as one tile in the mosaic rather than a verdict.
Late in life, Terman compared the most and least successful men in his own sample. The IQ of the two groups was practically identical. They differed in something else: drive, self-confidence, and the ability to follow through. The founder of the largest study of intelligence ever run concluded that success in life came down mainly to what his test had never measured.