Longitudinal Studies of Children’s Intelligence

1. Longitudinal Studies ofChildren’s Intelligence • IQ appears to be relatively stable from age 3 through adulthood. • Overall, retest correlations tend to be higher when: • The interval is shorter. • The older the children. • Correlation between IQ in latter preschool and grade school ranges from .6 to .8. Between adolescents, it increases to ~ .8.

2. Possible Reasons for IQ Stability • Overlap hypothesis - IQ is cumulative. • Overlap between current and past knowledge. • Environmental stability - People tend to remain in the same environments across the developmental life span. • Prerequisite Learning Skills – • Individual retains the same learning tools (e.g., problem-solving methods) from year to year. • Neurological Consistency-The pattern of neurological development remains relatively constant.

3. Evidence for the Instability of IQ • While overall IQ remains constant across large groups of individuals, specific individuals may exhibit large changes in IQ. • This may be due to changes such as dramatic shifts in environment or individual factors.

4. Instability of IQ(continued) • California Guidance Study (1948-12 year period): • 59% of children exhibited changes of > 15 points • 37% > 20 or more point • 9% > 30 or more points.

5. Instability of IQ (continued) • Garber Study (1988) • Generally, children in culturally disadvantaged environments lose IQ points whereas people in culturally enriched environments gain IQ points. • Specifically, examined the relationship between children reared in environments with mothers who had IQ’s either >80 or <80. • No difference, from 13-35 months (avg IQ = 95) but by 14, > 80 mothers = 90, whereas, < 80 mothers = 67.

6. Instability of IQ (continued) • Instability attributable to changes in: • Parental concern re: education. • Also, home environments characterized by “encouragement…structure” associated with increases in IQ. • Emotional dependency on parents was another factor responsible for IQ loss in childhood. • During school years, IQ increases were associated with high achievement drive, competitive striving, and curiosity about nature.

7. IQ in Early Childhood • Preschool tests have moderate predictive validity in predicting future IQ. • Between ages 2 and 14, the correlation is about .3. • Infant tests have little predictive validity (best for concurrent validity - relative status now). • Little correlation in scales even with intervals as small as 3 months. • The reason for these low correlations is the change in the construct of IQ.

8. IQ in Infancy(continued) • The construct of IQ in infancy is made up of largely motor development and visual-perceptional skills. • This differs from how intelligence is defined in school aged children. • In infancy, parental education and other characteristics of home environment are better predictors of subsequent IQ.

9. Early Childhood IQ (continued) • This speaks to the importance of early intervention programs that provide training in the prerequisite learning skills and the need for parental involvement. • Beyond 18 months, prediction of IQ is improved if tests are combined with family SES information. • However, infant tests may have higher predictive validities within non-normative samples.

10. Typical IQ instruments • Bayley Tests of Infant Development- 0-42 months. • Stanford-Binet V (2 through adulthood). • Wechsler Preschool and Primary Scales of Intelligence (2.5 years to 7.25 years). • Wechsler Intelligence Scale for Children-IV • (6 through 16-11 months).

11. Issues in the Assessment of Adult IQ Findings re: Age and IQ • In Cross-sectional designs, such as that used in Wechsler's standardization samples, IQ declines with age. • Possible explanations include: • Less education • Poorer health • Less familiarity with the information age.

12. Issues in IQ Assessment (continued) • Longitudinal designs involve testing one cohort (same individuals) at different times. • In contrast to cross-sectional designs, using longitudinal designs, IQ increases with age. • Explanation includes exposure to more information as one grows older.

13. Issues in IQ Assessment (continued) • In Cross-sequential designs, combination of longitudinal and cross-sectional using a time-lag design. • A time-lag design provides that same-age cohorts are tested at different time periods (e.g., 40-year-olds tested at 1970 and 1980). • That is, 20 years tested in 1940 are compared to themselves in 1970 and 20 year olds tested in 1970.

14. Cross-Sequential Findings • Older cohorts have higher IQ's from when they were tested earlier (IQ increases over time). • However, when different age groups were compared to one another at times (20 y.o. in 1950 vs. 20 y.o. in 1970), no significant differences emerged. • This suggests that experiential factors, not age itself, leads to changes in IQ.

15. Conclusions re: Changes in Adult IQ • True age decrements do not begin until well after age 60. • One exception is speeded tests which do decrease with age. • Overall changes in IQ in older age are largely related to health status. • That is, elderly individuals in poorer health do less well on tests of intelligence.

16. Conclusions (continued) • Test norms require frequent updating. • Experiential, cultural, variables must be taken into account in interpreting test scores. • IQ scores do measure cultural factors.