What is IQ?
The Intelligence Quotient (IQ) is a standardized measure of an individual's cognitive ability compared to the general population. The concept was developed by French psychologist Alfred Binet in 1905, originally to identify children who needed additional educational support.
The original formula was simple: mental age divided by chronological age, multiplied by 100. Today, modern tests use a standard deviation scale developed by David Wechsler in the 1950s, which remains the clinical reference standard.
IQ distribution in the population
The Wechsler scale defines:
- Mean: 100 points
- Standard deviation: 15 points
- 68% of the population falls between 85 and 115
- 95% of the population falls between 70 and 130
- 99.7% of the population falls between 55 and 145
This means an IQ of 130 places someone in the top 2% of the population — not the top 0.1%, as many assume.
What do IQ tests measure?
Standardized cognitive tests assess multiple components of intelligence:
- Fluid reasoning — the ability to solve novel problems without prior knowledge
- Crystallized reasoning — accumulated knowledge and vocabulary
- Working memory — the ability to hold and manipulate information in real time
- Processing speed — how quickly simple cognitive tasks are performed
- Visuospatial reasoning — understanding spatial relationships and visual patterns
The most widely used clinical test worldwide is the Wechsler Adult Intelligence Scale (WAIS-IV), administered by certified psychologists.
What IQ tests DON'T measure
This is the most important part — and the one most often overlooked.
Psychologist Howard Gardner proposed in 1983 his theory of Multiple Intelligences, arguing that human intelligence is multidimensional. An IQ test does not assess:
- Emotional intelligence — recognizing and managing your own and others' emotions
- Creative intelligence — lateral thinking and innovative capacity
- Practical intelligence — everyday problem-solving (what Sternberg called "tacit knowledge")
- Social competence — leadership, empathy, interpersonal communication
"IQ measures an important part of human intelligence, but it falls far short of measuring everything that matters." — Robert Sternberg, Yale University
Online IQ tests: are they reliable?
Quality online IQ tests use the same types of questions as standardized tests — Raven's matrices, number sequences, verbal analogies, and spatial reasoning.
What they can do:
- Provide a reasonable estimate of fluid and abstract reasoning
- Identify strengths and weaknesses across different cognitive areas
- Serve as a guiding indicator before a professional assessment
Limitations:
- They don't control for external factors (fatigue, distraction, emotional state)
- They don't replace a full neuropsychological evaluation
- Scores can vary by 10–15 points between sessions
The Flynn Effect: is intelligence increasing?
A fascinating phenomenon discovered by researcher James Flynn in 1984: average IQ scores have risen by about 3 points per decade throughout the 20th century in most developed countries.
Hypotheses include improved nutrition, more education, and exposure to more complex, cognitively stimulating environments. This effect appears to have slowed — or even reversed — in some Nordic countries in recent decades (Dutton & Lynn, 2013).
How to interpret your result
| Score | Classification | % of population |
|---|---|---|
| 130+ | Very Superior | 2.2% |
| 120–129 | Superior | 6.7% |
| 110–119 | Above Average | 16.1% |
| 90–109 | Average | 50% |
| 80–89 | Below Average | 16.1% |
| 70–79 | Borderline | 6.7% |
| Below 70 | Very Low | 2.2% |
A result in the average range does not define your potential. Factors like motivation, persistence, environment, and educational opportunities have a massive impact on academic and professional success — often more than IQ itself.
Scientific references
- Wechsler, D. (1955). Manual for the Wechsler Adult Intelligence Scale. The Psychological Corporation.
- Flynn, J.R. (1984). The mean IQ of Americans: Massive gains 1932 to 1978. Psychological Bulletin, 95(1), 29–51.
- Gardner, H. (1983). Frames of Mind: The Theory of Multiple Intelligences. Basic Books.
- Sternberg, R.J. (1985). Beyond IQ: A Triarchic Theory of Intelligence. Cambridge University Press.
- Dutton, E., & Lynn, R. (2013). A negative Flynn Effect in Finland. Intelligence, 41(6), 817–820.