In Chapter 6, Gould provides a brief overview of the science of factor analysis. As a process of “attempting to discover ‘underlying’ structure in large matrices of data,” factor analysis reveals positive, negative, and zero correlations between different measurements (268). These correlations (relationships) are measured by the correlation coefficient r; however, Gould notes that correlation shows a relationship, only, and does not indicate cause (270, 273). As a mathematical tool, researchers can identify multiple factors of measurement and reduce them into fewer dimensions (the first principal component and second principal component) in order to simplify relationships and arrive at a reasonable explanation of results through inference (275, 280). Gould also notes that the first principal component is a representation of a “mathematical abstraction” and “not a ‘thing’ with physical reality” (280).

Gould then introduces Cyril Burt (1883-1971), an educational psychologist and advocate for the statistical analysis of IQ tests. Both Burt and his mentor and predecessor, Charles Spearman, recognized the importance of using factor analysis in “provid[ing] a theoretical justification” for their belief in heritable and measurable intelligence (269). However, it was Charles Spearman who first identified a correlation coefficient (g), which he claimed was the “unitary quality underlying all cognitive mental ability” (281).