General Psychology Chapter 3

IQ Scores and Ranges

130+: Very Superior 120-129: Superior 110-119: High Average 90-109: Average 80-89: Low Average 70-79: Borderline Intellectual Disability <70: Intellectual Disability

Intelligence Quotient (IQ)

A measure of intelligence originally computed by dividing a person's mental age by his or her chronological age and multiplying the result by 100; it is now derived from norms provided for standardized intelligence tests

Heritability

A statistical estimate of the proportion of the total variance in some trait that is attributable to genetic differences among individuals within a group

Adoption IQ Studies

As adopted children grow into adolescence, the correlation between their IQ scores and those of their biologically unrelated family members diminishes and reaches zero by adulthood. Adopted children score higher on IQ tests than birth sibling who were not adopted (possibly due to enriched environment).

Important Facts About Heritability

Estimates apply only to a particular group living in a particular environment, do not apply to individuals. Traits can be modified by the environment.

Computing Heritability

Family traits can be misleading; adoption studies are more reliable; twin studies (monozygotic vs dizygotic)

Environmental Factors Associated with Reduced Mental Ability

Poor Parental Care Malnutrition Exposure to Toxins Stressful Family Circumstances

Twin IQ Studies

The scores of identical twins are always much more highly correlated than those of fraternal twins. Scores of identical twins reared apart are more highly correlated than those of fraternal twins raised together.

Fraternal (Dizygotic) Twins

Twins that develop from two separate eggs fertilized by different sperm; they are no more alike genetically than are any other pair of siblings

Identical (Monozygotic) Twins

Twins that develop when a fertilized egg divides into two parts that develop into separate embryos