measures of Gc are viewed as resulting from early investments of Gf. Subse-
quent domain knowledge acquisition and maintenance is a function of Gf
and Gc abilities, both as direct influences and indirectly through positive in-
fluences of Science/Math and Intellectual/Cultural trait complexes, and
through negative influences of Clerical/Conventional and Social trait com-
plexes. Not shown is an important developmental component, which is that
increments in domain knowledge will result in small, but significant incre-
ments in traditional measures of Gc (because such measures sample broadly
from many of the areas of domain knowledge—especially those that are gen-
eral to the wider cultural milieu). It is important to note that one key differ-
ence between the traditional Gc approach and the current approach is that
domain knowledge is envisioned to include many different areas that individ-
uals in a culture do not share, such as occupational knowledge and avoca-
tional knowledge. Thus, acquisition of domain knowledge in most areas
(such as technical jargon, or specific job-relevant information) will probably
have a very limited effect on traditional Gc measures.
EMPIRICAL DATA: TRAIT COMPLEXES
AND DOMAIN KNOWLEDGE
Although longitudinal data are necessary to test the developmental elements
of the PPIK theory, the cross-sectional data collected to date have provided
broad support for several aspects of the approach. Below we provide a few il-
lustrations of the results from these studies, in the context of basic age-related
patterns, and trait complex associations.
Age and Domain Knowledge
In a study of 228 adults between age 21 and 62, all of whom had achieved at
least a baccalaureate level of education, Ackerman (2000) administered a
large battery of traditional Gf and Gc ability tests, along with measures of
personality, interests, and self concept, to obtain trait complex measures. In
addition, 18 separate domain-knowledge scales were administered to the par-
ticipants. The domains included physical sciences and technology (e.g., chem-
istry, physics, biology, technology), civics (e.g., U.S. history, U.S. govern-
ment, economics), humanities (e.g., art, literature, music), and business (e.g.,
management, law). As would be expected from the extant abilities literature
(e.g., Horn, 1989), middle-aged adults performed on average, more poorly
than younger adults on Gf tests (rGF,age= –.39) and performed slightly better
on Gc tests (rGC,age= +.14). Scatterplots for these abilities and age are shown in
Fig. 5.2. A single composite of Gf and Gc that ignored domain knowledge
- TYPICAL AND MAXIMAL PERFORMANCE 129