Pearson correlations (mostly as phi coefficients) were computed between all item responses, separately for male and female data. Each correlation matrix was submitted to a principal components analysis. Four component factors were extracted from
each analysis and rotated using an oblique Promax rotation. In later years, a Direct Oblimin rotation replaced Promax. As Barrett and Kline (1980) showed using a UK Gallup sample of EPQ data collected by the Eysencks, incorporating two tests of factor extraction quantity, up to 9 first-order factors could be reliably extracted from a principal component analysis, but these always folded back to the expected four EPQ factors when a second-order analysis was undertaken. Further informal analyses showed that extracting four component factors at the first order produced virtually equivalent results as RG7420 manufacturer using a hierarchical procedure. This result added some confirmation that the fixed extraction quantity within the Eysenck analyses was sensible and ‘fit for selleck chemical purpose’. Following the component analyses and rotations, the male and female factor pattern matrices for a specific country were compared to their respective male and female UK reference- sample counterparts (these UK datasets had been analyzed using exactly the same
procedure as described above). The comparison was made using an orthogonal Procrustes solution published by Kaiser, Hunka, and Bianchini (1971). This procedure transformed each matrix (the target and comparison matrix) to an orthogonalized form prior to rotating the orthogonalized comparison matrix to the orthogonalized UK target matrix, utilizing a least-squares criterion to establish the optimal fit between the two matrices. The procedure reported the ‘target-comparison’ fit as a series of transformation cosines between each respective component factor from both matrices. These cosines were interpreted as congruence coefficients between the respective factors. The procedure also reported a ‘mean
solution cosine’ which was the average congruence computed across all 90 items, where each target item vector PAK6 was compared to its counterpart in the comparison matrix. Eysenck, Barrett, and Eysenck (1985) summarised the congruence results derived from 24 country comparisons, showing that all relevant UK-to-country comparisons averaged 0.983. Given the factor comparison analyses were adjudged satisfactory, the final stage of analyses were conducted. These established scale-mean comparisons between the UK and the country, while forming a score-key specific to a particular country. If extra items were included over and above the standard 90-item EPQ set, two further PCA analyses were undertaken which now included all items in a country dataset.