What is the Intelligence Quotient? Definition and Functioning
Understanding IQ, its calculation, its history, and its significance. A complete dive into the measurement of human intelligence and its multiple facets.
The intelligence quotient, commonly referred to as IQ, fascinates as much as it questions. This measure of intelligence, used for over a century, allows for the evaluation of an individual's cognitive abilities in relation to the general population. But what does this number really represent? How is it calculated? And above all, what does it really tell us about our intelligence?
🎯 Definition of the intelligence quotient
The intelligence quotient (IQ) is a standardized score designed to measure a person's cognitive abilities relative to their age group. It is a quantitative assessment of intelligence that takes into account several dimensions of human cognition.
Contrary to popular belief, IQ is not an absolute measure of intelligence. It is rather a relative indicator that positions an individual on a standardized scale where the average is set at 100, with a standard deviation of 15 points.
Standardized score
IQ compares your performance to that of a representative sample of the population
Age-adjusted
Tests are calibrated according to age groups for a fair comparison
Multidimensional
It assesses several facets: logical, verbal, spatial, working memory
💡 Good to know
The term "intelligence quotient" comes from the old calculation method that divided mental age by chronological age. Today, this formula is no longer used, but the name has remained. Modern tests use a method of statistical deviation.
🧠 Test your IQ for free
Evaluate your cognitive abilities with our online IQ test. 20 questions, 15 minutes, instant and detailed results.
Take the IQ test →📜 History of the intelligence quotient
The history of IQ begins in the early 20th century with the work of French psychologist Alfred Binet. In 1905, the Ministry of National Education entrusted him with a mission: to identify children needing special educational support.
Binet, in collaboration with Théodore Simon, then developed the first metric scale of intelligence. This scale introduced the concept of mental age: an 8-year-old child who passes the tests corresponding to a 10-year-old child has a mental age of 10 years.
The major milestones
1905 - Binet-Simon
Creation of the first intelligence scale in France for national education
1912 - Stern
The German psychologist William Stern invents the term "intelligence quotient"
1916 - Stanford-Binet
Lewis Terman adapts the test for the United States and standardizes it
1939 - Wechsler
David Wechsler creates the WAIS scale, still used today
"The scale, strictly speaking, does not allow for the measurement of intelligence, as intellectual qualities are not superimposable, and consequently cannot be measured like surfaces."
— Alfred Binet, 1905
⚠️ An important nuance
Alfred Binet himself was skeptical about the idea of fixed and measurable intelligence. He saw his test as a practical tool for identifying educational needs, not as a definitive measure of human potential. This nuance is often forgotten in discussions about IQ.
🔢 How is IQ calculated?
The method of calculating IQ has evolved significantly since the early tests. Today, tests use a statistical approach called deviation method.
The old formula (historical)
The original formula by Stern was simple: IQ = (Mental Age / Chronological Age) × 100. A 10-year-old child with a mental age of 12 years thus had an IQ of 120. This method posed problems as it did not work well for adults.
The modern method
Today, IQ is calculated by statistical comparison with a representative sample of the population of the same age. The score is adjusted so that:
- The average is exactly 100
- The standard deviation is 15 points
- The distribution follows a Gaussian curve (bell curve)
💡 What this means
With this method, your IQ score indicates where you stand compared to other people your age. An IQ of 115 means you scored better than about 84% of the reference population.
📏 The IQ scale explained
The IQ scale follows a normal distribution (Gaussian curve). Here’s how to interpret different scores:
| IQ Score | Classification | % of the population |
|---|---|---|
| 130 and above | Very Superior (HPI) | 2.3% |
| 120 - 129 | Superior | 6.7% |
| 110 - 119 | High Average | 16.1% |
| 90 - 109 | Average | 50% |
| 80 - 89 | Low Average | 16.1% |
| 70 - 79 | Borderline | 6.7% |
| Below 70 | Intellectual Disability | 2.3% |
⚠️ The HPI threshold
An IQ of 130 or above is the criterion set by the World Health Organization to qualify a person as High Intellectual Potential (HPI). This threshold corresponds to about 2.3% of the population, or about 1 in 44 people.
🎯 Where do you stand?
Discover your position on the IQ scale with our free online test. Detailed results by cognitive category.
Take the test now →🔬 What IQ really measures
Modern IQ tests assess several dimensions of cognitive intelligence. The Wechsler scales (WAIS for adults, WISC for children), global references, measure five main indices:
Verbal comprehension
Vocabulary, verbal reasoning, understanding of abstract concepts
Perceptual reasoning
Visual logic, spatial reasoning, solving non-verbal problems
Working memory
Ability to hold and manipulate information in the short term
Processing speed
Speed of executing simple cognitive tasks
Fluid vs crystallized intelligence
Psychologists distinguish between two types of intelligence measured by IQ tests:
- Fluid intelligence: the ability to solve new problems, independent of acquired knowledge. It tends to decrease with age.
- Crystallized intelligence: knowledge and skills acquired through experience and education. It remains stable or increases with age.
💡 Cognitive training
While fluid intelligence is more stable, cognitive abilities can be maintained and developed through regular brain training. Targeted exercises can improve working memory, attention, and processing speed.
⚠️ The limits of IQ
While IQ remains a valuable tool in psychology, it has important limitations that should be understood to correctly interpret results.
What IQ does not measure
Emotional intelligence
The ability to understand and manage one's emotions and those of others
Creativity
The ability to generate original and innovative ideas
Social intelligence
Interpersonal skills and the ability to adapt socially
Motivation & perseverance
The qualities that allow potential to be transformed into success
Potential biases
- Cultural biases: some tests may favor specific cultural references
- Effect of anxiety: stress can significantly affect performance
- Testing conditions: fatigue, environment, emotional state influence results
- Practice effect: familiarity with tests can improve scores
⚠️ IQ is not destiny
Many studies show that IQ explains only part of success in life. Motivation, perseverance, opportunities, social environment, and emotional intelligence play equally important, if not more important, roles in certain areas.
📈 Can we improve our IQ?
This question is the subject of much research. While IQ is relatively stable in adulthood, several studies suggest that certain factors can positively influence it.
Scientifically proven factors
Education
Each additional year of education can increase IQ by 1 to 5 points
Physical activity
Regular exercise improves brain oxygenation and cognitive functions
Quality sleep
Sleep is essential for memory consolidation and cognitive performance
Cognitive training
Targeted exercises can improve specific abilities such as working memory
💡 Brain training with JOE
The app JOE - Your Brain Coach offers over 30 cognitive games designed to stimulate memory, attention, logical reasoning, and processing speed. Regular training of 15 minutes a day can help maintain and develop your cognitive abilities.
What to remember
Rather than seeking to "increase one's IQ," it is more relevant to aim for the overall development of cognitive abilities. Brain training, continuous learning, a healthy lifestyle, and regular intellectual stimulation allow for maintaining a high-performing brain throughout life.
🚀 Boost your cognitive abilities
Train your brain daily with JOE, your brain coach. Over 30 scientifically designed games to stimulate all your cognitive functions.
First test your IQ →Discover JOE →
✅ Testing your IQ: the different options
Several options are available to assess your intelligence quotient, each with its advantages and limitations.
Professional tests
Tests administered by psychologists (WAIS-IV for adults, WISC-V for children) remain the reference. They last about 2 hours and provide a detailed analysis of your cognitive abilities. Average cost: 200 to 400€.
Online tests
Online tests offer a first accessible and practical estimate. While they do not replace a professional assessment, they allow for evaluating performance across the main dimensions of cognitive intelligence.
Speed
15 to 30 minutes are enough to obtain an indicative result
Accessibility
Free and available immediately, without appointment
First evaluation
Ideal for an estimate before a professional assessment
💡 Our recommendation
Start with our free online IQ test for a first evaluation. If the results raise questions or if you need an official diagnosis (especially for HPI detection), consult a psychologist for a complete assessment.
🎯 Conclusion
The intelligence quotient remains a valuable tool for assessing certain dimensions of cognitive intelligence. Understanding what it measures — and what it does not measure — allows for its wise use, without overestimating or underestimating it.
Let us remember that human intelligence is much richer and more complex than a simple number. Your IQ does not define who you are, nor what you can achieve. Creativity, emotional intelligence, perseverance, and social skills are equally essential for success and fulfillment.
The key is to continue stimulating your brain, learning, and developing throughout life. It is this dynamic of growth that constitutes the true richness of human intelligence.
Ready to discover your cognitive abilities?
Take our free IQ test and start your brain training with JOE.
