MUCH OF WHAT we know about intelligence has originated from psychometrics. Other psychological traits, such as human personality, have also been the object of study of psychometrics. In this chapter, we will look back at the roots of psychometrics and its current development for the evaluation of personality and cognitive abilities. About the question of one or many ‘intelligences’, we will overview how several models arrange abilities in a hierarchical way. Intelligence quotient (IQ) tests will be discussed, as well as the meaning and existence of the g factor. We will cover the major developments in item response theory and adaptive tests, as they will prove key for the rest of the book. Finally, we will briefly touch on some of the heated debates, such as the nature versus nurture dilemma, the analysis of group differences, the Flynn effect and the way variously gifted and disabled people affect psychometric theory and testing.

TELLING IDIOTS SAVANTS APART

The oldest accounts of formal systematic psychological testing are said to have originated in China about three millennia ago. The assessment of candidates for public service officers comprised the ‘six skills’, the ‘six conducts’ and the ‘six virtues’ (Rust and Golombok, 2009). At the beginning of the seventh century ce, an “essentially open competitive examination took place annually or every three years, [with gradually] adjusted examinations [that] were based on general learning rather than specific or technical knowledge” (Teng, 1943). These procedures were borrowed for Western academic and civil recruiting during the seventeenth and eighteenth centuries.

Recruiting was just one of the motivations behind the birth of modern psychological testing. During the second half of the nineteenth century psychological testing was further elaborated as a tool to understand and improve children's mental development and education, to detect the intellectually ill or disabled and to ascertain how the principles of evolution, adaptation and individual differences emerged in the realm of psychological traits.