The Magnitude and Components Change in the Black-White IQ Difference from 1920–1991: A Birth Cohort Analysis of the Woodcock-Johnson Standardizations

Intelligence, Vol. 35, 2007.


The black-white difference in test scores for the three standardizations of the Woodcock-Johnson battery of cognitive tests is analyzed in terms of birth cohorts covering the years from 1920 through 1991. Among persons tested at ages 6-65, a narrowing of the difference occurred in overall IQ and in the two most highly g-loaded clusters in the Woodcock-Johnson, Gc and Gf. After controlling for standardization and interaction effects, the magnitude of these reductions is on the order of half a standard deviation from the high point among those born in the 1920s to the low point among those born in the last half of the 1960s and early 1970s. These reductions do not appear for IQ or Gc if the results are restricted to persons born from the mid-1940s onward. The results consistently point to a B-W difference that has increased slightly on all three measures for persons born after the 1960s. The evidence for a high B-W IQ difference among those born in the early part of the 20th century and a subsequent reduction is at odds with other evidence that the B-W IQ difference has remained unchanged. The end to the narrowing of the B-W IQ difference for persons born after the 1960s is consistent with almost all other data that have been analyzed by birth cohort.