The second strand of interpersonal theory is the principle of rigidity, which contends that within diagnoses of personality type on the interpersonal circumplex, vector length (a measure of statistical deviance) is an index of psychopathology (psychiatric deviance; Wiggins, Phillips, & Trapnell, 1989). In general, people with rigid, inflexible personalities have more problems--even if such people are inflexible in a friendly direction--while people with flexible, adaptive personalities have fewer problems--even if such people are generally more hostile than friendly.