10 Intelligence and Aptitude · 10.1 Intelligence and aptitude
10.1.2 Measuring intelligence and aptitude; giftedness and intellectual disability
Intelligence tests began with Binet and Simon (1905), gave us mental age and the IQ = MA ÷ CA × 100, and moved to Wechsler's deviation IQ (mean 100, SD 15); aptitude tests predict how well a person can learn a particular skill; at the two ends of the IQ curve stand the gifted (about 130 and above) and the intellectually disabled (IQ below 70, with poor adaptive behaviour, starting before 18).
- APPSC Paper I
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Core facts
- The B.Ed.-level basics (Binet-Simon, Stern, Terman, Wechsler scales, verbal/non-verbal, individual/group tests, Terman's old IQ table): see EDU-ID-01. Slow learners, Terman's gifted study, Renzulli, education of the gifted and the RPwD Act: see EDU-ID-03. This note adds what the Psychology Paper II asks.
- Francis Galton: first tried to measure intelligence through sensory and reaction-time tests (anthropometric laboratory, London, 1884). James McKeen Cattell coined the term "mental test" (1890).
- Alfred Binet (with Theodore Simon) built the first intelligence test, 1905, to find Paris children who needed special schooling.
- Mental age (MA): the level of performance of an average child of a given age; brought in with the 1908 revision. Binet and Simon took a child whose MA was two years below his chronological age as retarded (2023 key).
- William Stern (1912) proposed the mental quotient; Lewis Terman used IQ in the Stanford-Binet (1916).
- IQ = (MA ÷ CA) × 100. Multiplying by 100 is done to avoid decimals (2023 key). MA 12, CA 10 → IQ 120.
- Deviation IQ (Wechsler): a person's score compared with others of the same age, scaled to mean 100, SD 15: IQ = 100 + 15z. One SD above the mean = 115; two SD below = 70.
- Wechsler scales: Wechsler-Bellevue 1939, WISC 1949 (children), WAIS 1955 (adults), WPPSI 1967 (pre-school). Gave a verbal, a performance and a full-scale IQ.
- Army Alpha (verbal) and Army Beta (non-verbal), USA, 1917, group tests for recruits, under Robert Yerkes.
- Culture-fair tests: Raven's Progressive Matrices (1938), Cattell's Culture Fair Intelligence Test, Goodenough's Draw-a-Man test (1926).
- Indian tests: C.H. Rice (Hindustani Binet, 1920s), V.V. Kamat (Binet in Kannada and Marathi, 1930s), C.M. Bhatia's Battery of Performance Tests (1955), A.J. Malin's Intelligence Scale for Indian Children (MISIC, an adaptation of WISC), S.S. Jalota's group test.
- Aptitude = a set of characteristics showing a person's potential to acquire a specific skill with training (Bingham). Aptitude + interest give the best chance of success.
- Aptitude tests: special (one area) and multiple aptitude batteries: Differential Aptitude Tests (DAT, Bennett, Seashore and Wesman, 1947; Indian adaptation by J.M. Ojha) and the General Aptitude Test Battery (GATB, US Employment Service, 1947).
IQ classes and share of people (NCERT, Wechsler-type labels)
| IQ | Description | Share |
|---|---|---|
| above 130 | very superior | 2.2% |
| 120–130 | superior | 6.7% |
| 110–119 | high average | 16.1% |
| 90–109 | average | 50.0% |
| 80–89 | low average | 16.1% |
| 70–79 | borderline | 6.7% |
| below 70 | intellectually disabled | 2.2% |
- Giftedness: exceptional general ability shown across many areas; usually IQ above 130. Talent: a remarkable ability in one specific field (music, sport).
- Gifted children show: advanced reasoning and questioning; fast information processing; good generalisation; originality; long attention span; strong recognition memory; high intrinsic motivation; independent, non-conformist thinking; liking for solitary academic work. Conformist thinking is not a trait (2023 key).
- Intellectual disability (old term mental retardation), AAMD/AAIDD: significantly below-average intellectual functioning (IQ about 70 or below) together with deficits in adaptive behaviour, appearing in the developmental period (0 to 18 years) (2023 keys: IQ below 70; 0–18).
- AAMD = American Association on Mental Deficiency → AAMR (1987, Mental Retardation) → AAIDD (2007, Intellectual and Developmental Disabilities).
Levels of intellectual disability
| Level | IQ (about) | Share of cases | What the person can do |
|---|---|---|---|
| Mild ("educable") | 50/55–70 | about 85% | school skills to about class 6; work, live independently, marry and raise a family with little support |
| Moderate ("trainable") | 35/40–50/55 | about 10% | self-care, speech, simple routine work in sheltered settings |
| Severe | 20/25–35/40 | 3–4% | basic self-care and simple speech after long training; close supervision |
| Profound | below 20/25 | 1–2% | constant care; little or no speech; often physical problems too |
Explained
1. Ratio IQ vs deviation IQ
| Ratio IQ | Deviation IQ | |
|---|---|---|
| Formula | MA ÷ CA × 100 | 100 + 15 × (score − age mean) ÷ age SD |
| Meaning | pace of mental growth | standing among age-mates |
| Works for adults? | no: MA stops rising in mid-teens | yes |
| Used by | early Stanford-Binet | Wechsler, all modern tests |
Example of the adult problem: a 40-year-old with an adult-level MA of 16 would get IQ 40 by the ratio formula; the deviation IQ avoids this by comparing him only with other 40-year-olds.
2. Reading a deviation IQ on the normal curve. About 68% of people score 85–115, about 95% score 70–130, and about 99.7% score 55–145. IQ 115 ≈ 84th percentile; 130 ≈ 98th; 70 ≈ 2nd.
3. Kinds of tests, with the right example
| Kind | Who it suits | Example |
|---|---|---|
| Individual verbal | literate person, diagnosis | Stanford-Binet, Wechsler verbal |
| Individual performance | young, illiterate, deaf, other language | Kohs blocks, Alexander pass-along, Bhatia |
| Group verbal | quick screening of literates | Army Alpha, Jalota |
| Group non-verbal | mixed or illiterate groups | Army Beta, Raven's matrices |
Individual tests are more accurate and diagnostic; group tests are cheaper and quicker but give less information about one person. Culture-fair tests cut down language and schooling, but no test is fully free of culture: even pictures and puzzles are more familiar to some groups.
4. Intelligence, aptitude, achievement, interest
| Test | Measures | Looks | Example |
|---|---|---|---|
| Intelligence | general mental ability | broad, future | WAIS, Raven's |
| Aptitude | potential in one area | future (with training) | DAT, clerical test |
| Achievement | what has been learnt | past (after training) | class test, board exam |
| Interest | likes and dislikes | choice of field | Strong, Kuder inventories |
5. Aptitude tests in more detail
- Special aptitude tests: mechanical (Bennett Mechanical Comprehension Test), clerical (Minnesota Clerical Test: checking numbers and names fast), musical (Seashore Measures of Musical Talents, 1919), artistic (Meier Art Judgment Test), and tests for teaching, medicine, law and engineering entrance.
- DAT, eight sub-tests: verbal reasoning, numerical ability, abstract reasoning, clerical speed and accuracy, mechanical reasoning, space relations, spelling, language usage. A profile of eight scores is used in educational and vocational guidance (choice of stream or job).
- Uses: selection for jobs and courses, placement and training, career counselling, and in correctional homes, vocational training matched to an inmate's aptitude.
6. Intellectual disability: the three parts of the definition
- Intellectual functioning well below average: about two SD below the mean (IQ about 70, allowing 70–75 for test error).
- Adaptive behaviour deficits in conceptual (language, money, time), social (relationships, following rules, avoiding being cheated) and practical (self-care, work, travel, safety) skills. Measured by scales such as the Vineland Social Maturity Scale (Edgar Doll, 1935), which gives a social quotient (SQ) = social age ÷ CA × 100; Indian adaptation by A.J. Malin.
- Onset in the developmental period, before 18.
A low IQ alone is not enough: a person with IQ 68 who manages daily life, work and money well is not diagnosed. DSM-5 (2013) sets the level (mild to profound) by adaptive functioning, not by IQ alone.
7. Causes of intellectual disability
- Genetic / chromosomal: Down syndrome (trisomy 21; the most common chromosomal cause), fragile X syndrome (the most common inherited cause), phenylketonuria (PKU) (preventable by diet if screened at birth).
- Prenatal: maternal infections (rubella, toxoplasmosis), alcohol (fetal alcohol syndrome), drugs, malnutrition, iodine deficiency (cretinism), radiation.
- Perinatal: lack of oxygen at birth, very premature birth, birth injury.
- Postnatal: meningitis, encephalitis, head injury, lead poisoning, severe malnutrition, gross social and cultural deprivation.
Most mild cases have no single known biological cause and are linked with poverty and deprivation; most severe and profound cases have a clear organic cause.
8. Helping each group
- Gifted: acceleration, enrichment, mentoring, special programmes (detail in EDU-ID-03); watch for boredom, under-achievement and isolation.
- Intellectually disabled: early identification and stimulation, special or inclusive education with an individual plan, vocational training and sheltered workshops, behaviour modification for self-care, family counselling. The RPwD Act 2016 lists intellectual disability (including specific learning disabilities and autism spectrum disorder in its Schedule) among the 21 disabilities.
Common traps
- ✗ "IQ = CA ÷ MA × 100." ✓ IQ = MA ÷ CA × 100; × 100 is there to avoid decimals.
- ✗ "Terman built the first intelligence test." ✓ Binet and Simon, 1905; Terman made the Stanford-Binet, 1916.
- ✗ "Ratio IQ works for adults." ✓ It fails after the mid-teens; adults get a deviation IQ (mean 100, SD 15).
- ✗ "Aptitude tests measure what has already been learnt." ✓ That is achievement; aptitude predicts future learning with training.
- ✗ "DAT is a test of general intelligence." ✓ DAT is a multiple aptitude battery (8 sub-tests).
- ✗ "AAMD cut-off is IQ 75–80." ✓ Below 70 (about 2 SD below the mean), plus adaptive-behaviour deficits.
- ✗ "The developmental period for diagnosis is 0–16 years." ✓ 0–18 years (standard answer).
- ✗ "Moderately disabled people hold jobs and raise families." ✓ That is mild ("educable"); moderate = "trainable", sheltered work.
- ✗ "Gifted children are conformist thinkers." ✓ They are independent, non-conformist thinkers.
- ✗ "Raven's matrices is a verbal test." ✓ Non-verbal, culture-fair group test.
Quick revision
- Galton 1884 sensory tests; J.M. Cattell "mental test" 1890; Binet-Simon 1905; MA 1908.
- Binet: MA two years below CA = retarded; Stern 1912 quotient; Terman Stanford-Binet 1916 "IQ".
- IQ = MA ÷ CA × 100 (× 100 avoids decimals); deviation IQ mean 100, SD 15.
- Wechsler-Bellevue 1939, WISC 1949, WAIS 1955, WPPSI 1967; Army Alpha (verbal) and Beta (non-verbal) 1917.
- Culture-fair: Raven's 1938, Cattell CFIT, Draw-a-Man; India: Bhatia 1955, MISIC, Jalota.
- Aptitude = potential with training (future); achievement = past learning; DAT 8 sub-tests, GATB.
- Average 90–109 (50%); above 130 very superior/gifted; below 70 intellectually disabled (2.2% each).
- ID = IQ below 70 + adaptive deficits + onset before 18 (AAMD → AAMR → AAIDD).
- Mild 50–70 educable, independent living; moderate 35–50 trainable; severe 20–35; profound below 20.
- Causes: Down syndrome, fragile X, PKU, rubella, alcohol, iodine lack, birth asphyxia, deprivation.
Go deeper: Deeper (beyond what APPSC Paper I usually asks)
Deeper Advanced
1. Changing definitions of the age limit. The AAMD/AAMR definitions and DSM-IV used onset before 18, which is the standard exam answer. The AAIDD's 12th manual (2021) moved the limit to before 22, and DSM-5 says only "during the developmental period". Answer 18 unless a question names the 2021 AAIDD manual.
2. Gifted: definitions beyond IQ. The US Marland Report (1972) named six areas: general intellectual ability, specific academic aptitude, creative or productive thinking, leadership, visual and performing arts, and psychomotor ability. With Renzulli's three rings and Gardner's intelligences, this is why identification uses teacher nomination, products, creativity and achievement tests and not one IQ score.
3. Limits of IQ testing. IQ predicts school marks well (correlation about 0.5) but job success and life outcomes less well; scores carry measurement error (always read a band, e.g. 95–105); tests can be biased against groups with different language or schooling; and a label ("dull", "retarded") can become a self-fulfilling prophecy. Average IQ scores rose about 3 points per decade in the 20th century (Flynn effect), so old norms over-rate today's test takers; tests must be re-normed.
4. Aptitude testing in selection. Multiple aptitude batteries replaced one IQ score in guidance because people have uneven profiles (intra-individual differences). Their weakness: the sub-tests correlate with one another, so the differences between sub-test scores are less reliable than each score alone.
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