Is g an entity? A Japanese twin study using syllogisms and intelligence tests

Chizuru Shikishima, Kai Hiraishi, Shinji Yamagata, Yutaro Sugimoto, Ryo Takemura, Koken Ozaki, Mitsuhiro Okada, Tatsushi Toda, Juko Ando

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


Using a behavioral genetic approach, we examined the validity of the hypothesis concerning the singularity of human general intelligence, the g theory, by analyzing data from two tests: the first consisted of 100 syllogism problems and the second a full-scale intelligence test. The participants were 448 Japanese young adult twins (167 pairs of identical and 53 pairs of fraternal twins). Data were analyzed for their fit to two kinds of multivariate genetic models: a common pathway model, in which a higher-order latent variable, g, was postulated as an entity; and an independent pathway model, in which the higher-order latent variable was not posited. These analyses revealed that the common pathway model which included additive genetic and nonshared environmental factors best accounted for the three distinct mental abilities: syllogistic logical deductive reasoning, verbal, and spatial. Both the substantial g-loading for syllogism-solving, historically recognized as the symbol of human intelligence, and the emergence of g as an entity at an etiological level, that is, at the genetic and environmental factor level, provide further support for the g theory.

Original languageEnglish
Pages (from-to)256-267
Number of pages12
Issue number3
Publication statusPublished - 2009 May


  • Common pathway model
  • Independent pathway model
  • Multivariate genetic analysis
  • Syllogism
  • Twin study
  • g

ASJC Scopus subject areas

  • Experimental and Cognitive Psychology
  • Developmental and Educational Psychology
  • Arts and Humanities (miscellaneous)


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