“…Specifically, attrition decreases the validity of the inferences that can be drawn about treatment efficacy, as it can alter random composition of groups, reduce statistical power, limit the generality of findings, and introduce sampling bias (Armbruster & Kazdin, 1994). Second, premature treatment termination has a negative financial impact on the mental health service system by decreasing cost-effectiveness, as missed and cancelled appointments decrease staff productivity and cause an increase in unit cost for services (Garfield, 1994;Larsen, Nguyen, Green, & Attkisson, 1983;Pekarik, 1985). These problems have led some to identify poor treatment attendance as the most important issue facing psychotherapy researchers (e.g., Phillips, 1985).…”