Re: Association between side-impact airbag deployment and risk of injury.

The study compared injury outcome by match pairing sided airbag (SAB) deployment versus no SAB deployment vehicles using 2000 to 2009 CIREN (Crash Injury Research Engineering Network) and NASSCDS (National Automotive Sampling SystemYCrashworthiness Data System) database. The study then concluded that head SAB was protective, whereas thoracic SAB was not. The authors suggested that this could be explained by possible occupant’s frailty or by seat posture. However, before I can reach my own definitive conclusion, I would like the authors to elaborate some comments I have with the methodology. First, in matching car crash between SAB deployment versus no SAB deployment, was the study not inherently implying that the groups could never be equal based on an imparted energy (IE) principle (IE = delta v + principal direction of force) because one would have assumed that for an airbag to be deployed, a certain IE would be required? Can the authors elaborate in general what would trigger SAB to deploy, how reliable was this triggering mechanism, and has the mechanism changed or improved during the course of the new model car? Second, in using the same IE principle, most of the variables matched in the study (age, sex, occupant seating position, vehicle model year and body type, etc.) all belonged tovehicle 1 (V1), the impacted vehicle (table 1 in the article). What happened to the vehicle 2 (V2) data, particularly the vehicle type, shouldn’t that be matched as well? How could one evenmatch the correctV1with the correct V2, maybe using V1/V2 weight ratio? Last, it appeared from table 1 that no SAB deployment vehicles had a trend toward a higher delta v and a higher intrusion, a somewhat contradictory finding considering that the SAB-deployed vehicles should have had a higher delta v and intrusion. Why was that? What was the reason SAB was not deployed, perhaps unit malfunction, belowthreshold delta v, or impact?Will the authors be able to discern this information from the data why airbag was not deployed because this may have significant implications to the consumer as well as to the authors’study final conclusion? In conclusion, I thank the authors in advance for clarifying these few comments. I greatly appreciate and enjoy the authors’ work and look forward for the authors’ continued effort research in this area.