IQ and Measurement
IQ and Measurement
Intelligence quotient expresses a person's mental age as a proportion of chronological age, multiplied by 100. William Stern gave the formula and Lewis Terman popularised it in the Stanford-Binet test. An IQ score is a comparison with peers, not a fixed measure of worth.
The formula and the classification
IQ = (Mental Age / Chronological Age) x 100
A child of 10 years who performs like an average 12-year-old has an IQ of 120. The broad bands used are:
| IQ range | Category |
|---|---|
| Above 140 | Genius or near genius |
| 120-140 | Very superior |
| 110-120 | Superior |
| 90-110 | Average or normal |
| 80-90 | Dull normal |
| 70-80 | Borderline |
| Below 70 | Intellectual disability |
Types of intelligence tests
- Individual tests are given to one person at a time — Stanford-Binet, the Wechsler scales.
- Group tests are given to many at once — the Army Alpha and Army Beta of the First World War.
- Verbal tests need language; non-verbal tests use figures, and performance tests use materials such as blocks — Bhatia's Battery is the well-known Indian performance test.
- Non-verbal and performance tests are used for young children, non-readers and children whose school language differs from their home language.
What makes a test trustworthy
Three qualities are asked about repeatedly. Reliability means the test gives a consistent score when repeated. Validity means it measures what it claims to measure. Norms are the scores of a large representative group against which an individual is compared, and objectivity means different scorers reach the same result. A test can be perfectly reliable and still invalid, which is why a well-set but badly aimed test is worse than no test.
Limits a teacher must respect
- An IQ score is only as good as the test's fairness to that child's language and culture.
- It predicts school performance moderately and life success weakly.
- It says nothing about creativity, motivation, emotional intelligence or practical skill.
- Labelling a child by a score damages self-image and lowers teacher expectation — a self-fulfilling prophecy.
The concept of mental age was introduced by Alfred Binet, who built the first practical intelligence test in 1905 with Theodore Simon to identify children needing extra help — the original purpose was support, not sorting.
✗ A low IQ score means the child cannot learn. | ✓ It means the child scored below peers on that test; teaching method, language and support all change outcomes.
संकेत: बुद्धि-लब्धि (IQ) = मानसिक आयु ÷ वास्तविक आयु × 100; मानसिक आयु की कल्पना बिने ने दी थी।
Expect one question, either a direct calculation or a matching item on test types. Practise the formula both ways — you may be given IQ and chronological age and asked for mental age. The repeated trap in test-type questions is calling Bhatia's Battery a verbal test; it is a performance battery designed for Indian conditions. Remember Binet gave mental age, Stern gave the IQ ratio, Terman standardised it at Stanford, and Wechsler introduced separate verbal and performance scales.
Frequently asked questions
How is IQ calculated?
IQ equals mental age divided by chronological age, multiplied by 100. A child of eight whose test performance matches an average ten-year-old has a mental age of ten and an IQ of 125.
Which intelligence test is suitable for a child who cannot read?
A non-verbal or performance test such as Bhatia's Battery or Raven's Progressive Matrices, because these use figures, blocks and patterns instead of language and so do not penalise the child for reading ability.
Why should teachers be careful with IQ scores?
Because a score depends on the test's language and cultural fairness, ignores creativity, motivation and practical ability, and can become a label that lowers both the child's self-image and the teacher's expectations.
60-second recap
- IQ = mental age divided by chronological age, times 100.
- Binet gave mental age; Stern gave the ratio; Terman standardised Stanford-Binet.
- Tests: individual or group; verbal, non-verbal or performance.
- Bhatia's Battery is an Indian performance test for non-readers.
- A score is a comparison, not a verdict — never label a child by it.