school grade-point average, performance on an
intelligence test, an SAT-type mathematics test,
and an adult reading comprehension test. This
set of tasks surely exhausts the variance attributable
to any general ability construct; and, as
one would expect, we found that general ability
accounted for a substantial proportion of variance
in the composite measure of general
knowledge. Next we entered a composite measure
of exposure to television, but it did not
account for any additional variance. However, a
composite index of reading volume accounted
for a substantial 37.1 percent of the variance
when entered after the four ability measures
and television exposure.