A Fresh Set of Survival Risk Ratios Derived from Incidents in the National Trauma Data Bank from which the ICISS May Be Calculated

Abstract

Survival risk ratios (SRRs) are database-specific point estimates of survival associated with each injury International Classification of Diseases, Ninth Revision (ICD-9) code. They are derived for each injury code by dividing the number of patients who survive the code by the total number of patients that display the code. SRRs are used to measure injury severity and distribution and are most prominently featured in the ICD-9 Injury Severity Score (ICISS), which is the product of a patient’s SRRs. Because SRRs are important for trauma scoring, it is important that they be derived from a representative trauma population. The purpose of this study was to compare a new set of SRRs derived from the National Trauma Data Bank (NTDB) with SRRs derived years ago from the North Carolina Hospital Discharge Database (NCHDD). Tests for differences of proportions were applied to determine which ICD-9 codes have significantly different SRRs in an attempt to characterize the database differences. Two different ICISSs were calculated for 170,853 eligible patients using the two different sets of SRRs, NCHDD and NTDB. The NTDB SRRs were calculated and applied using a 10-fold cross-validation to avoid bias in estimation. Estimates of discrimination for both ICISSs were calculated using the area under the receiver-operating characteristic curve. R2 and Akaike information criterion statistics were compared. A modest statistical case is made for using the NTDB SRRs rather than the NCHDD SRRs. Researchers should begin using the NTDB SRRs for their outcome modeling and for ICISS calculation.