CLASS 12

Intelligence Tests (IQ)

HISTORY 1. Binet’s Mental age (MA) 2. Stern’s Ratio formula for IQ 3. Deviation formula for IQ

Ratio formula IQ = (MA/CA) x 100 MA=mental age CA=chronological age

PROS AND CONS Can compare across ages Average=100 Problem

Example: Martha’s two sons Dieter Wolfie Mental age Chronological age IQ

example Dieter Wolfie Mental age 7 Chronological age 5 IQ

example Dieter Wolfie Mental age 7 Chronological age 5 IQ 140

example Dieter Wolfie Mental age 7 6 Chronological age 5 IQ 140

example Dieter Wolfie Mental age 7 6 Chronological age 5 IQ 140 100

Deviation formula Separate calculations for each age group Set average = 100 for each group Similar to using percentiles to compare students from different schools

PROS AND CONS Can compare across ages Drawback – hides real differences

Bell Curve of IQ scores < 9.4>

Mental retardation -70 or below -morons, imbeciles, and idiots Giftedness -130 or above

Validity of intelligence tests Some famous tests: -Stanford-Binet -WISC -WAIS Generally successful: reliable and valid

Representative views: Nature vs. Nurture Representative views: 1. Mostly genetic: Rushton, Eysenck, Jensen 2. All environment: Kamin 3. It’s 50-50: Scarr

Nature: Genetic Influences on IQ - estimating heritability 1. Twin studies 2. Adoption studies

Identical Twins

Fraternal Twins

Logic of Twin Studies Do twins match up on a trait? e.g. same eye color; intelligence Usually identical twins match up better than fraternal twins. Why? - identical twins share 100% of genes - fraternal twins share 50% of genes Use heritability formula (see textbook)

Sample heritability values Eye color (100%) Shoe color (8%) Personality (40-60%) Intelligence (50-80%)

Nurture: Environmental influences Twin & Adoption studies also confirm impact of nurture 1. Group differences 2. Economic differences 3. Test bias

Culture-Free Tests -- designed to avoid language handicap -- e.g., Raven’s matrices

More examples See course web site