The measurement of extroversion: A comparison of the Eysenck Personality Inventory and the Eysenck Personality Questionnaire

The authors of the Eysenck Personality Inventory (EPI) and the Eysenck Personality Questionnaire (EPQ) have claimed that the extraversion scales contained in the two tests are equivalent. Although scores on the two scales are moderately highly correlated, supplementary analyses suggest that they differ in at least one important respect. While the EPI scale measures extraversion as a reasonable mix of impulsivity and sociability, the EPQ's scale is almost purely a measure of sociability. Recent experimental evidence demonstrates that impulsivity is responsible for several findings previously attributed to extraversion. This evidence raises serious doubt about the usefulness of the EPQ extraversion scale in experimental research on extraversion.