Before revision: The Cattell–Horn–Carroll theory is an integration of two previously established theoretical models of intelligence: the Gf-Gc theory of fluid and crystallised intelligence (Cattell, 1941; Horn 1965), and Carroll's three-stratum theory (1993), a hierarchical, three-stratum model of intelligence.
After revision: The Cattell–Horn–Carroll theory is an integration of two previously established theoretical models of intelligence: the Gf-Gc theory of fluid and crystallized intelligence (Gf-Gc) (Cattell, 1941; Horn 1965), and Carroll's three-stratum theory (1993), a hierarchical, three-stratum model of intelligence.