Validity, reliability and implications of an index of inpatient severity of illness

We discuss statistical characteristics of AS-SCORE, a recently developed index of illness severity for medical patients. The acronym "AS-SCORE" indicates the five major attributes of the index: age, system involved, stage of the disease, complications and response to therapy. The reliability of both the four-class system (k = .84) and the additive point scoring system (r = .92) was substantiated by two judges who independently classified and scored 105 records. We also tested the content validity of the four-class system and found that as severity increased there was a concomitant increase in hospital charges, laboratory charges, length of stay, number of consultations and mortality rates. In addition, we performed a regression analysis to determine the relative contributions of each of the attributes to the AS-SCORE value. We describe how we used the AS-SCORE severity of illness index to compare physician practice patterns and we suggest several other potential uses. We concluded that the AS-SCORE index is a reliable, valid and useful prototype method to assess differences in severity of illness for medical patients.