One problem lies in evaluating the effectiveness of this policy because of the inadequacies of methodologies that estimate crime reduction effects on the basis of past offender behaviors or predictions of future offender behavior. In addition, identification of chronic offenders (CO's) is problematic, and a definition of CO's has not been agreed upon. Another issue to be considered is the staggering increase in prison construction and operation costs that would result and the difficulty in evaluating cost-effectiveness. The impact of selective incapacitation on the police and courts is also difficult to assess. Finally, the policy raises important ethical and constitutional issues. Therefore, implementation of a selective incapacitation policy should be limited.