Feasible quantitative data, which is uniform across mental health service units, is necessary for a service system management's efforts to direct the improvement of the system. A procedure for starting with available data and progressively evolving evaluative data and the service system cost/effectiveness is introduced in the context of one state's intramural mental hospital system. Ten years of data on pristine admissions to one state's hospitals of child and adolescent patients and on these patients' subsequent state hospitalization are used to illustrate the beginning of the procedure