to mathematically identify a small set of dimensions (factors) that
can be used to reconstitute each of a larger set of variables. Each
variable in the larger set is described as a weighted linear compos-
ite of the factors. Thus a score on any variable in the larger set can
be reproduced from scores on the factors. Using factor analysis, the
U.S. Employment Service, for example, was able to reproduce
scores on more than seventy skill measures from just ten factors,
leading to the development of the General Aptitude Test Battery
(GATB; U.S. Department of Labor, 1970). As the result of further
development (test validation studies), the GATB can now be used,
not just to describe P’s skills but to predict P’s potential (aptitude)
for many different occupations, which can be differentiated by their
configuration of skill requirements.
In PEC theory, these skill factors are seen as dimensions under-
lying all human skills, extant and still to come. These dimensions
are termed abilities,following conventional usage (Carroll, 1993).
Thusabilitiesare defined in PEC theory as reference dimensions for
the description of skills. They are usually measured by ability tests
and typically grouped together in an ability test battery.
Studies in ability testing have shown that there are at least three
types of abilities: (1) perceptual (including acuity and speed of per-
ception; perception of detail, form, depth, and motion in the sev-
eral sense modalities), (2) cognitive (including speed and fluency of
comprehension, memory, reasoning, and judgment in verbal, numer-
ical, and spatial modalities), and (3) motor or psychomotor (includ-
ing speed, fluency, dexterity, strength, and coordination in small- or
large-muscle modalities). There might be a fourth type, not well
studied, called affective abilities, which include emotional control,
empathy, emotional mimicry (as in acting), emotional production
on demand, and so on. The first three types of abilities appear to
underlie response skills, whereas affective abilities might underlie
reinforcement skills.
Another way to categorize abilities is in terms of (1) input, (2)
central processing, and (3) output. All behavior (for example,
skills) consists of input, central processing, and output components.
444 CAREER CHOICE AND DEVELOPMENT