In 1999, a merging of the Gf-Gc theory of Cattell and Horn with Carroll's Three-Stratum theory has led to the Cattell–Horn–Carroll theory (CHC Theory).
I 1999 har en sammensmeltning af Cattell og Horns Gf-Gc teori med Carrolls Tre-Stratum teori ført til Cattell-Horn-Carroll teorien.