Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

Intelligence and Educability 93
(if any at all). . . . Siblings (and parent-child pairs) share some
environmental elements (for example, general atmosphere of
intellectual encouragement) as well as genes in common. However,
whatever the factors that determine IQ change over age,
apparently they are not simply the general family intellectual
climate available to each sibling. Rather, one might speculate
that the salient variables are relatively more specific events and
intellectual circumstances wrhich quite possibly interact with
age, personality, social, and motivational factors.
The simplex growth model also predicts that individuals with
higher genetic intelligence (i.e., higher C values in the model)
should show greater intra-individual variability in measured IQ
over the course of development. This was actually found to be
the case in the data of Honzik et al. (see Table 3.3). A recent
analysis of these data showed that children with the greatest
year-to-year fluctuations in IQ manifested also a general upward
trend in IQ and had the higher mean IQ over the course of
development (Honzik and Gedye, personal communication).
ACHIEVEMENT AS A FUNCTION OF STUDY TIME
Carroll (1963) proposed a model of school learning in which the
degree of learning, or amount learned, is a function of the ratio of
time actually spent in learning to the time needed to learn. Time
spent in learning is defined as the smallest value of either (a) time
allowed for learning, (b) length of time the learner is willing to
persevere, or (c) the amount of time needed to learn up to some
criterion of mastery. The model can be expressed as follows:
a r t • r f t*12 spent \
Amount of Learning = / ---------—-
\time needed J
The time needed to learn a given amount of material or skill up
to some criterion of proficiency is a function both of the type or
quality of the instruction and of the learner’s ability. The amount
of time actually spent will be a function of the time allowed by
the teacher or by other circumstances external to the learner (such
as the number of hours in the school day and the amount of time
the parents may require the child to spend at his homework or in
being tutored) and also of the amount of time the learner car