Science of Intelligence

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By Psychometrica

What are intelligence and IQ

Intelligence vs IQ

First, let’s go over some basic definitions so that we have a shared understanding of certain concepts.

Intelligence can be defined as a property of the mind that encompasses many interrelated abilities such as the capacities to reason, to plan, to solve problems, to think abstractly, to comprehend ideas, to use language, and to learn new things.

It is important to note that intelligence is not about how much knowledge or expertise a person has; rather, it is about how fast a person is able to acquire knowledge and expertise as well as how well a person is able to perform new kinds of tasks.

The IQ (intelligence quotient) is a measurement of intelligence. IQ presumes that there are differences in intelligence among the people of a population. It expresses, with one numeric score, how intelligent a person is in relation to the rest of the population.

Is the concept of intelligence worthwhile? How about IQ tests?

As you might have guessed, there is no full scientific consensus on this issue – although we all know that scientists disagree about numerous issues!

What problems do some experts point out? Many contend that intelligence does not relate to cognitive abilities and therefore criticize IQ tests for not measuring intelligence.

This criticism is not completely unfounded. It is true that intelligence is not clearly defined, nor is it easily measured. By contrast, other human dimensions (height, weight, muscular strength) are self-defining and can be measured objectively.

However, we can make certain indisputable statements about IQ and intelligence:

  • A general cognitive ability exists, and human beings differ in how much of it they possess.
  • All standardised tests of academic aptitude measure this cognitive ability to some degree, but IQ tests, which were designed expressly for that purpose, measure it the most accurately.
  • IQ scores match well with what people mean when they use the word “intelligent”.
  • Properly designed and administered IQ tests are not demonstrably biased against social, economic, ethnic, or racial groups.

IQ predicts various forms of success

Criticism of IQ tests can be countered by the successful use of IQ as a predictor of success in various domains.

Although IQ is not a perfect predictor of academic or work success, even critics recognize that there is a strong correlation between IQ and many forms of success. This means that a higher IQ is generally associated with higher achievements. What kind of achievements do we mean here?

IQ → academic success

The IQ test was originally designed as a predictor of school children’s academic success. Only later, in the 20th century, was its use extended to the workplace and other contexts.

While it is true that there are many diverse factors at play, IQ has repeatedly been shown to have a high correlation with academic success.

IQ → professional success

IQ can partially predict success at work. Measuring job candidates’ IQ and considering IQ in the recruitment decision is a useful tool. However, the use of IQ tests in the work setting is even more controversial than using them in the academic setting.

Fewer than 50% of employers worldwide use IQ tests as a means of evaluating job candidates, although there are significant differences between countries:

55% → China and Spain
30% → India and France
3% → U.S and Germany

Scientific research suggests that while an IQ test is not a perfect predictor of the future success of a job applicant, and while many other factors are relevant to work success, IQ should indeed be considered.

This is because the candidate’s IQ has a high correlation with future success at work. Recently, researchers compared the effectiveness of various methods of selecting employees: IQ tests, unstructured interviews, personality tests, and biographical questionnaires. The result was clear: IQ is the single best predictor of work success.

According to Schmidt and Hunter, “for hiring employees without previous experience in the job, the most valid predictor of future performance is intelligence.” IQ test scores predict performance ratings in all occupations. The effect is the strongest for military training and high-complexity jobs but lower for low-complexity jobs and, surprisingly to some, leadership roles.

That said, for highly qualified intellectual activities (research, management) low IQ scores are more likely to be a barrier to adequate performance, whereas for physical professions, athletic strength (manual strength, speed, stamina, coordination) is more likely to influence performance.

We can also find support for IQ’s usefulness in Justin Menkes’ article published in the Harvard Business Review titled “Hiring for Executive Intelligence”.

Menkes states: “Despite the very real shortcomings, IQ tests are still a better predictor of managerial success than any other assessment tool. The business world’s reluctance to use intelligence testing of any kind has robbed companies of a powerful tool for evaluating candidates for employment or promotion.”

IQ → wealth

As IQ correlates with success at work, it also does with income and wealth. In essence, the higher your IQ, the more likely you are to have a higher income, accumulate more wealth, and attain a greater social status.

Self-made millionaires’ average IQ is estimated to be around 115. Meanwhile, self-made billionaires’ average IQ is estimated to be around 120.

IQ → life outcomes

IQ has also been found to correlate with various life outcomes, although it remains uncertain whether their relationship with IQ is direct or rather caused by high-IQ individuals on average disposing of more wealth.

For instance, higher-IQ people are less likely to die in traffic accidents. In Sweden, higher IQ was found to correlate with decreased risk of mortality in adult men and therefore higher longevity.

The table above shows some astonishing facts about the relation of IQ to various life experiences:

  • A person with a low IQ is 6 times more likely to be unemployed than a person with a high IQ.
  • A person with a low IQ is almost 3 times more likely to divorce within 5 years after marriage than a person with a high IQ.
  • A person with a low IQ is 10 times more likely to go to jail than a person with a high IQ.
  • A person with a low IQ is 15 times more likely to live in poverty than a person with a high IQ.

What do we know about intelligence?

This shouldn’t come as a surprise: there are many definitions of intelligence.

The American Psychological Association defines it as follows:

Individuals differ from one another in their ability:

  • to understand complex ideas,
  • to adapt effectively to the environment,
  • to learn from experience,
  • to engage in various forms of reasoning,
  • to overcome obstacles by thinking.

Although these individual differences can be substantial, they are never entirely consistent: a given person’s intellectual performance will vary:

  • on different occasions,
  • in different domains,
  • as judged by different criteria.

All concepts of “intelligence” that scientists have come up with are attempts to clarify and organise this complex set of phenomena. Although considerable clarity has been achieved in some areas, no conceptualization has yet answered all the important questions and none is universally agreed on.

Indeed, when two dozen prominent theorists were recently asked to define intelligence, they gave two dozen somewhat different definitions!

Scientific conclusions about IQ

There are many rumors about intelligence – as well as many false claims and half-truths circling around. In 1994, prominent researchers on intelligence decided to combat this state of affairs. They came together and published all the factual knowledge they could gather about intelligence. The following are their conclusions.

Their definition of intelligence, which was published in “Mainstream Science on Intelligence” and signed by 52 intelligence researchers in 1994, claims:

“Intelligence is a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings – “catching on”, “making sense” of things, or “figuring out” what to do.”

Intelligence can be measured, and intelligence tests measure it well. They are among the most accurate (in technical terms: reliable and valid) of all psychological tests and assessments.

While there are different types of intelligence tests, they all measure the same intelligence. Some use words or numbers and require specific cultural knowledge, while others do not – instead, they use shapes or designs and only require knowledge of simple, universal concepts.

The distribution of people along the IQ continuum, from low to high, can be represented well by the bell curve. Most people cluster around the average IQ of 100. Few are either very bright or very dull: about 3% of Americans score above IQ 130 and about the same percentage – below IQ 70.

Practical importance of IQ

IQ is strongly related to many important educational, occupational, economic, and social outcomes – probably more so than any other single measurable human trait.

Its relation to the welfare and performance of individuals is:

  • very strong in some areas such as education and military training,
  • moderate but robust in others such as social competence,
  • modest but consistent in others such as law-abidingness.

Whatever it is that IQ tests measure, it is of great practical and social importance.

A high IQ is an advantage in life because virtually all activities require some reasoning and decision-making skills. Of course, a high IQ does not guarantee success, just like a low IQ does not guarantee failure in life. There are many exceptions, but the odds for success in our society greatly favor individuals with a higher IQ.

The practical advantages of having a higher IQ increase as life settings become more complex (novel, ambiguous, changing, unpredictable, or multifaceted). For example, a high IQ is generally necessary to perform well in highly complex or fluid jobs (white-collar professions, management). It is a considerable advantage in moderately complex jobs (crafts, clerical, and police work), but it provides less advantage in settings that require only routine decision making or simple problem solving.

Differences in intelligence are certainly far from being the only factor affecting performance in education, training, and highly complex jobs, but intelligence is often the most important one.

Certain personality traits, special talents, aptitudes, physical capabilities, experiences and the like are important for successful performance in many jobs, but they have narrower applicability or “transferability” across tasks and settings compared with general intelligence.

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