GROUP SCORES IN IQ STABLE OVER TIME
Individual's test score remains relatively stable after approx 6 yrs of age
- Evidence: 3rd grade boys reassessed 10yrs later: r = 0.72
- 13yr-olds reassessed at 18yrs: r = 0.78
- 3yr-olds reassessed at 4yrs: r = 0.83
- 3 yr-olds reassessed at 12 yrs: r = 0.46
The longer the time frame, the weaker the relationship.
Shorter time frames hold true.
16-18+ yrs of age: the IQ stays more constant.
IQ's do vary within individuals BUT as a group, the correlations do remain fairly consistent after about 16-18yr-olds.
Group Scores In IQ Stable Over Time
What are the Implications?
Good predictive validity of the tests, or
Predictive validity of IQ test is confounded with stability in environment of longitudinal samples
Why isIQ more stable with age?
Cumulative nature of intellectual development - It's easier to build on foundations
Prerequisite learning skills - prior learning supports your ability to continue to learn & gives you flexibility of thought & problem-solve more effectively.
What about individual differences?
Does everyone remain stable?
Individual scores over time can be more unstable.
California Guidance Study (n=222)
- 6y vs 18y (test-retest correlations high) .6
- 59% chn increased > 15 IQ points
- 37% chn Increased >20 IQ points
- 9% chn increased > 30 IQ points
Why? e.g.an enriched environment
Can we use thst kind of enriched environment to improve everybody's IQ?!
FACTORS AFFECTING A CHILD'S INTELLECTUAL DEVELOPMENT
Change in family structure/home/and or change in parent's economic status
Severe or prolonged illness, or poor home conditions
Therapeutic, remedial or counselling programs
Enriched educational programs
NB Not blanket statements for all children.
INSTABILITY?STBILITY IN INDIVIDUAL'S IQ
Capron & Duyme (1989):
2x2 design for adopted chn.
- High/low SES-biological parents x high/low SES-adopted parents.
Children reared by high SES parentsIncreased IQ.
Change enhances IQ INDEPENDENT of SES of biological parent
SES of biological still had some effect.
LONGITUDINAL STUDIES AND INDIVIDUAL'S IQ
In low SES groups, IQ's decline from the baseline over time without early intervention
- In high SES groups, IQ's increase from baseline over time.
RISK FACTORS OF INTELLIGENCE
The Rochester Longitudinal Study
Sameroff et al. (1987)
1987 4yr (n=215)
1993 13yr (n=152)
Identified 10 risk factors for lower IQ
Mother history mental illness
Mother didn't go to high school
Mother severs anxiety
Mother rigid attitudes
Few mother-child interactions
Head of household semi-skilled job
> 4 siblings
Father not living at home
Child belongs to a minority group
Family > 20 stressful events in child's first 4 years.
CHILDREN WHO HAD 4 OF THESE RISK FACTORS AT AGE 4 - HAVE AN IMPACT ON IQ.
Intelligence and Age
WAIS:Raw scores are on subsets - the standardized IQ score according to norms.
Standardised in 9 age groups between 16 and 74 on adult intelligence scales
Mean is always 100
1 Standard Deviation is always 15
* 96% of all people will fall within 30 points of 100 (b/n 70 & 130)
* 68% of people score within 15 points above or below 100 (85 -115)
* 14% people (115 -130 & 70-85)
* 2% 130 +
* 2% below 70.
Cross-sectional analysis of age-related changes in IQ
Kaufman et al. (1989)
- Verbal IQ scores remain stable with age (crystallized)
- Non-verbal IQ scores show a decline (fluid intelligence)
IQ and Age
Age does not make your IQ drop.
Test results are standardized.
Therefore, these are a refelection of the age group.
You may see a drop in intellect.
Fluid intelligence declines after mid 30's (standardised)
Crystallized less so but a decline evident (standardised)
Slide 18 graph