CLASS 12
Intelligence Tests
(IQ)
HISTORY
THREE STEPS:
1. Binet’s Mental age
2. Stern’s Ratio formula
3. Terman’s Deviation formula
ALFRED BINET
FRANCE (1900): How to evaluate children?
Mental age
-analogy to physical age
-evaluated by performance
William Stern
• GERMANY 1912
Ratio Formula
IQ = (MA/CA) x 100
MA=mental age
CA=chronological age
PROS AND CONS
1. Can compare across ages
2. Average=100
3. Problem
Example: Martha’s two sons
Dieter
Mental age
Chronological age
IQ
Wolfie
example
Dieter
Mental age
7
Chronological age
5
IQ
Wolfie
example
Dieter
Mental age
7
Chronological age
5
IQ
140
Wolfie
example
Dieter
Wolfie
Mental age
7
8
Chronological age
5
8
140
100
IQ
LEWIS TERMAN
(CALIFORNIA 1916)
Deviation formula
- Separate calculations for each age
group
- Set average = 100 for each group
- Set S.D. = 15
PROS AND CONS
1. Can compare across ages
2. 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
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
- heritability (0 to 100%)
1. Twin studies
2. Adoption studies
Identical
Twins
Fraternal
Twins
Logic of Twin Studies
Twins tend to match up on many traits
e.g. same eye color; intelligence
BUT identical twins match up better than
fraternal twins.
Why?
- identical twins share 100% of genes
- fraternal twins share 50% of genes
Calculations
1. Calculate correlation between pairs of
twins:
-in identical twins
-among fraternal twins
2. Enter in Heritability Formula (see textbook)
Yields value between 0 and 100%
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