Wake Forest University School of Medicine, Medical Center Blvd,. Winston-Salem, NC 27157. 2. Virginia Tech â Wake Forest University Center for Injury. Biomechanics ... National Automotive Sampling System (NASS) data (crash data), but ...
A POPULATION-BASED COMPARISON OF CIREN AND NASS CASES USING SIMILARITY SCORING Joel D. Stitzel1,2, Patrick Kilgo3, Brian Schmotzer3, H. Clay Gabler2, J. Wayne Meredith1 1
Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157 2 Virginia Tech – Wake Forest University Center for Injury Biomechanics, Medical Center Blvd, Winston-Salem, NC 27157 3 Emory University, Atlanta, GA 30322
ABSTRACT The Crash Injury Research and Engineering Network (CIREN) provides significant details on injuries, and data on patient outcomes that is unavailable in the National Automotive Sampling System (NASS). However, CIREN cases are selected from specific Level I trauma centers with different inclusion criteria than those used for NASS, and the assertion that a given case is similar to the population of NASS cases is often made qualitatively. A robust, quantitative method is needed to compare CIREN to weighted NASS populations. This would greatly improve the usefulness and applicability of research conducted with data from the CIREN database. Our objective is to outline and demonstrate the utility of such a system to compare CIREN and NASS cases. This study applies the Mahalanobis distance metric methodology to determine similarity between CIREN and NASS/CDS cases. The Mahalanobis distance method is a multivariate technique for population comparison. Independent variables considered were total delta V, age, weight, height, maximum AIS, ISS, model year, gender, maximum intrusion, number of lower and upper extremity injuries, and number of head and chest injuries. The technique provides a unit-independent quantitative score which can be used to identify similarity of CIREN and NASS cases. Weighted NASS data and CIREN data were obtained for the years 2001-2005. NASS cases with Maximum AIS 3 resulted in a subset of 1,869 NASS cases, and 2,819 CIREN cases. Results of the analysis demonstrate the utility of the distance technique to identify similarity of CIREN cases with the average NASS case. All NASS means were within 10% of CIREN and higher except Total Delta V was 9% higher for CIREN, CIREN cases were 50/50 male:female, and mortality of CIREN cases was 38% lower than for NASS/CDS. Results demonstrate that on average the
CIREN cases analyzed had a greater proportion clustered about the mean distance for NASS cases than did the NASS cases, with a very similar average distance (similarity score) of 3.75. Maximum distance (worst similarity score) was 14.75. The mean peak in probability density for CIREN (0.37) is slightly higher than for NASS (0.34). The distribution in the main body for both datasets is unimodal and nearly symmetric, and the overall distribution is slightly skewed right. For body region specific injuries, similiarity increases then decreases gradually with increasing number of injuries for distance scores between 1 and 2. Maximum AIS similarity increases and then begins to decrease with a minimum distance of about 1.5. Distance is very high (9) for very low age (
