Assumptions underlying police applicant psycholocical screening are that a relatively high percentage of pathological persons are attracted to policing and that psychological screening can ensure a high quality of police performance. There is no research evidence, however, that police applicants are more pathological than applicants for other occupations or that there is a global 'police personality.' Neither has the validity of psychological testing in ensuring high quality police performance been established. The gap between practice and research findings in this area is due largely to the use of the 'engineering' model in applied social research. In this model, the social engineer accepts the client's definition of the problem and agencies' proposed needs at face value. Underlying values and resulting assumptions are disregarded. The 'clinical' model of applied social research, on the other hand, involves questioning assumptions underlying clinical appraisals. The clinical model recognizes that organizational goals and resistance to change are important factors in creating gaps between policy and research findings. Some organizational goals served by police psychological screening are support for police misconduct as based in individual pathology rather than organizational influences and also a symbolic sign to the community that the department is serious about securing high quality personnel. 27 references.