<P> Direct oblimin rotation is the standard method when one wishes a non-orthogonal (oblique) solution--that is, one in which the factors are allowed to be correlated . This will result in higher eigenvalues but diminished interpretability of the factors . See below . </P> <P> Promax rotation is an alternative non-orthogonal (oblique) rotation method which is computationally faster than the direct oblimin method and therefore is sometimes used for very large datasets . </P> <P> Charles Spearman pioneered the use of factor analysis in the field of psychology and is sometimes credited with the invention of factor analysis . He discovered that school children's scores on a wide variety of seemingly unrelated subjects were positively correlated, which led him to postulate that a general mental ability, or g, underlies and shapes human cognitive performance . His postulate now enjoys broad support in the field of intelligence research, where it is known as the g theory . </P> <P> Raymond Cattell expanded on Spearman's idea of a two - factor theory of intelligence after performing his own tests and factor analysis . He used a multi-factor theory to explain intelligence . Cattell's theory addressed alternate factors in intellectual development, including motivation and psychology . Cattell also developed several mathematical methods for adjusting psychometric graphs, such as his "scree" test and similarity coefficients . His research led to the development of his theory of fluid and crystallized intelligence, as well as his 16 Personality Factors theory of personality . Cattell was a strong advocate of factor analysis and psychometrics . He believed that all theory should be derived from research, which supports the continued use of empirical observation and objective testing to study human intelligence . </P>

Who is credited with promoting the use of factor analysis and why