Future research, for instance, should consider using additional measures of the FFM. The predominant measure in existing research is the NEO PI-R; and for good reason, as it has considerable empirical validation and a strong research foundation (Costa & McCrae, 1992; Widiger & Trull, 1997). The SIFFM and FFMRF facet assessments were modeled explicitly after the NEO PI-R (Mullins-Sweatt et al., 2006; Trull & Widiger, 1997). Nevertheless, reasonable questions have been raised regarding this particular structure for the FFM, including the selection and placement of facet scales (Saucier & Goldberg, 2002). An alternative measure that contains quite different facet scales is the HEXACO Personality Inventory (HEXACO-PI; Lee & Ashton, 2004, 2006). The first five scales of the HEXACO-PI align very closely with domains of the FFM (the HEXACO-PI includes a sixth scale assessing honesty-humility which they argue does not belong within agreeableness). It would be of interest for future research to compare the NEO PI-R and HEXACO-PI with respect to FFM PD relationships. For instance, schizotypal PD measures might correlate with the HEXACO-PI openness facet of unconventionality (contrary to the
