Variations in Psychological Attributes
Measuring intelligence
Explain the uses and misuses of intelligence tests.
Nature or nurture? Both. Twin and adoption studies show that identical twins have very similar intelligence even when raised apart, so heredity matters. But children adopted into enriched homes gain in intelligence, so environment matters too. Heredity sets a range; environment decides where within it a person ends up.
Measuring intelligence: in 1905, Alfred Binet and Theophile Simon made the first intelligence test, and introduced mental age (MA): the level of a person's mental ability compared with others of the same age.
In 1912, William Stern devised the Intelligence Quotient (IQ):
IQ = (Mental Age ÷ Chronological Age) × 100
Example: a 10-year-old (CA = 10) with a mental age of 12 has IQ = 12/10 × 100 = 120. The average IQ is 100, and IQ scores follow a normal (bell-shaped) curve: about half the population scores between 90 and 109.
At the two ends:
- Below 70: intellectual disability, with four levels: mild, moderate, severe and profound. It means difficulty in learning and in everyday adaptive skills, showing up before age 18.
- Above 130: giftedness.
Kinds of tests:
| Basis | Types |
|---|---|
| Number tested | individual or group |
| Form | verbal (needs reading), non-verbal (pictures and symbols, like Raven's Progressive Matrices) or performance (handling objects, like Kohs' block design test) |
| Culture | culture-fair or culture-biased |
Indian tests include Mohsin's Hindi intelligence test and Bhatia's Battery of performance tests. NCERT has a National Library of Educational and Psychological Tests (NLEPT).
Misuse: labelling a child as 'dull' from one test can stigmatise them and lower their own and others' expectations. IQ numbers must be used with care.
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