“…Additional support for the claim that these observations comprise evidence (however unsystematic) of potential artifact may be garnered from a large related literature showing that volunteer subjects in experimental and social psychology are likely to differ from nonvolunteers on a variety of demographic, personality, cognitive, and even physiological variables (Cooperman, 1980;Doty & Silverthorne, 1975;Dumas, 1978;Joe et al, 1977;Masling et al, 1981;Rosenthal & Rosnow, 1975;Sanders et al, 1977). Unfortunately, only a handful of recent studies have even indirectly addressed this volunteer issue in a clinical context, and many of these are questionably useful analogue designs using normal or quasi-clinical subjects.…”