Are IQ Tests Good Measures of Intelligence?

Are IQ tests good measures of intelligence? Yes—decades of research show they strongly predict school, job success, health, and more. Discover why IQ tests work and their limits.

Dr. Russell T. WarneChief Scientist

IQ tests have been used for over a century to measure intelligence, but they remain controversial. Critics argue that IQ tests are biased, culturally unfair, or too narrow in what they measure. Supporters point to decades of research showing that IQ tests are among the most scientifically sound psychological assessments ever created.

What IQ Tests Actually Measure

IQ tests measure our broad mental capability through various tasks that require thinking, reasoning, and problem-solving. These tasks might include vocabulary questions, pattern completion, mental arithmetic, spatial puzzles, or working memory challenges. Importantly, there is no single task that appears on every IQ test. Charles Spearman called this principle "the indifference of the indicator." He believed that any task that requires judgment, reasoning, or thinking, would measure intelligence to some degree. Modern research has confirmed that Spearman was correct.

The Evidence That IQ Tests Work

The strongest argument for IQ tests is their ability to predict real-world outcomes. IQ scores correlate strongly with school grades and standardized test scores, both in childhood and through college. In the workplace, higher IQ predicts how quickly people can be trained for jobs and how well they perform once trained. This relationship holds across virtually all occupations.

Beyond education and employment, IQ correlates with health and longevity. People with higher IQ scores tend to live longer and have better physical health, even after controlling for socioeconomic factors. Higher income, lower rates of criminal behavior, and more stable marriages are also associated with higher intelligence. There are exceptions; both high-functioning autism and anorexia are more common in people with higher IQ, but the general pattern is clear.

Perhaps most compelling is that IQ scores correlate with biological variables. Higher IQ is associated with larger brain size, more efficient brain functioning, faster reaction times, and specific DNA variants. If IQ tests were measuring nothing real or meaningful, these biological correlations wouldn't exist.

What IQ Tests Don't Measure

Acknowledging that IQ tests effectively measure intelligence doesn't mean they capture everything important about a person's mind or capabilities. IQ tests focus on cognitive abilities, the capacity to reason, solve problems, and think abstractly. They don't directly assess creativity, motivation, personality traits, or domain-specific knowledge. A high IQ opens doors, but hard work, conscientiousness, and emotional stability determine whether someone walks through them.

This is why comprehensive IQ test batteries report multiple scores and an overall IQ plus subscores for verbal reasoning, spatial ability, working memory, processing speed, and other specific cognitive abilities. This approach recognizes that while general intelligence (g) is important, other cognitive abilities contribute to success in school, the workplace, and life.

The Question of Bias

One common criticism is that IQ tests are biased against certain groups, particularly racial and ethnic minorities or people from disadvantaged backgrounds. Average IQ score differences do exist across demographic groups. However, the existence of group differences is not, by itself, evidence of test bias.

Test bias occurs when a group has a systematic advantage or disadvantage for reasons unrelated to what the test is measuring. Since the 1960s, IQ tests have been extensively studied for bias, and by the 1980s, screening for bias became standard practice before tests are released to the public. The overwhelming conclusion from this research is that professionally developed IQ tests are not biased, as long as they are used on the populations they were designed for.

Problems arise when tests are used inappropriately, such as administering tests designed for native English speakers to recent immigrants, or using tests normed in wealthy countries in impoverished nations with weak educational systems. The responsibility falls on test administrators to ensure that a test is appropriate for each examinee.

For a deeper dive into the nuances of what makes an IQ test biased, watch:

Are There Better Alternatives?

Some critics propose abandoning IQ tests in favor of alternative assessment tests of multiple intelligences, emotional intelligence, or practical intelligence. While these concepts are intriguing, the tests based on them face significant challenges.

Some people propose using personality tests instead of IQ tests for predicting job performance and other life outcomes. However, studies that compare the predictive power of personality tests and IQ tests consistently show that IQ is the better predictor of job performance and life outcomes. This is not to say that personality is irrelevant; IQ just matters more.

Other replacements for IQ have been proposed, but -- like personality -- they usually underperform as a predictor of job performance or life outcomes. For example, many people claim that emotional intelligence is more important for life success than intelligence. But the evidence does not support this popular claim. Moreover, emotional intelligence tests provide little or no unique information because they seem to just be rehashes of personality tests.

In the realm of job performance, the most consistent variable that surpasses IQ in predicting job performance is a work sample. Employers can collect this by asking for a portfolio or giving a standardized task to applicants to perform. The drawback to this strategy is that it is not suitable for entry-level jobs (when applicants do not have any job experience) or for promoting people to a new position where they would have new job duties. Additionally, it is sometimes impractical to get work samples from employees (e.g., if they work in a service industry that provides no tangible products), or work products may not be able to be shared because of nondisclosure agreements or other secrecy reasons. In these cases, IQ tests are still the best tool available for predicting job performance.

IQ Tests in the Real World

Professionally developed IQ tests are used extensively because they provide valuable information for important decisions. In schools, they help diagnose learning disabilities and identify students who may benefit from gifted programs. In clinical settings, they assist with psychological assessments and treatment planning. In employment, they help predict training success and job performance. In research, they have contributed to our understanding of human cognition more than almost any other psychological measure.

IQ tests are powerful tools that can help students succeed in school, employers find the best workers, and provide insight to examinees about their cognitive strengths and weaknesses. But it is important to recognize the limits of IQ. Even when IQ is the best single predictor available, predictions using IQ are usually improved by supplementing IQ with other variables, like personality, interests, and motivation. Just as it is an error to ignore IQ when making important decisions, it is also an error to expect IQ to do too much. IQ tests are one tool in a powerful arsenal of psychological assessment, and society benefits the most when the entire array of psychological tests are used appropriately.

Author

Dr. Russell T. WarneChief Scientist

Contact

Article Categories