Discovery Of General Intelligence
Intelligence tests were originally created with the practical goal of identifying students in need of alternative education (Binet & Simon, 1916). Because intelligence tests were originally devised to predict school grades, the items were intentionally designed to measure a general ability to profit from explicit instruction, concentrate on task, and engage in intellectual material. Indeed, research shows that such a general ability does seem to exist. Over a century ago, Spearman (1904) discovered that when a wide range of cognitive tests that have explicit instructions and require effortful concentration is administered to a diverse group of people, all of the tests tend to be positively correlated with one another, a finding often referred to as a "positive manifold." Spearman labeled the factor on which all individual tests loaded g, for general intelligence.
Over the past 100 years, the existence of g as a statistical phenomenon is one of the most replicable findings in all of psychology (Carroll, 1993; Chabris, 2007; Jensen, 1998).
Binet, A., & Simon, T. (1916) The development of intelligence in children (E. S. Kite, Trans.). Baltimore, MD: Williams & Wilkens.
Spearman, C. (1904). "General intelligence," objectively determined and measured. American Journal of Psychology, 15, 201-293.
Carroll, J. B. (1993). Human cognitive abilities: A survey of factor-analytic studies. Cambridge, UK: Cambridge University Press.
Chabris, C. F. (2007). Cognitive and neurobiological mechanisms of the Law of General Intelligence. In M. J. Roberts (Ed.), Integrating the mind: Domain general vs. domain specific processes in higher cognition (pp. 449-491). New York, NY: Psychology Press.
Jensen, A. R. (1998). The g factor: The science of mental ability. Westport, CT: Praeger.
from "The Cambridge Handbook of Intelligence"
Quoted on Wed Dec 21st, 2011