Kibeom Lee and Michael C. Ashton began development of the HEXACO model of personality structure in 2000, after cross-cultural research using the same lexical measures that gave us the Big Five began to show a sixth facet of personality. The addition of this sixth factor changed several of the existing factors of the five-factor model. It also integrated several items that did not fit well with the five-factor model and provided further evidence for the idea of reciprocal and kin altruism
The honesty-humility factor (and the HEXACO model in general) is only moderately correlated with the Big Five model of personality, but is highly correlated with the agreeableness factor of the Revised NEO Personality Inventory (NEO-PI-R), which is one of the factors of the five-factor model of personality. This correlation is mainly due to the Straightforwardness and Modesty subscales of the NEO-PI-R. However, forcing the NEO-PI-R to extract separate factors for honesty and agreeableness allows experimenters to better predict social adroitness and self-monitoring.[4]
Another study found that adding the HEXACO honesty-humility factor to personality measures improves predictive validity for both self- and other-reports of personality, and that simply creating an honesty factor from the FFM measures improves predictive validity for some measures (mainly social adroitness and sexuality measures), but not all (e.g. materialism and delinquency), which indicates that the HEXACO model is a better measure of personality than either the Big Five or the FFM