IIHS Advisories | No. 15, December 1993
Media distort HLDI data on injury claim frequencies for airbags
Several newspapers recently have published articles in which data from the Highway Loss Data Institute (HLDI) have been misused, and information about air bags and drivers' use of safety belts in cars equipped with air bags has been wrong. The Institute and HLDI would like to set the record straight and correct any misconceptions about air bags these news reports may have caused.
Flawed Study Results in Wrong Conclusions
George Hoffer, a Virginia Commonwealth University economics professor, has been misunderstanding HLDI data, and, as a result, drawing erroneous conclusions about air bags. The Institute has documented Hoffer's misuse of HLDI results over the past three years. In the most recent case, articles in the Wall Street Journal, the Detroit News, and Best's Insurance Management Reports cite a Hoffer study that is yet unpublished and apparently unavailable to other researchers. Using published HLDI results on overall insurance injury claim frequencies in cars with and without air bags, Hoffer's purported finding is that claims go up when air bags are installed. Contrary to what Hoffer says, however, injury claim frequencies don't always increase.
Injury claim frequencies for cars newly equipped with air bags are sometimes higher and sometimes lower than those registered by the same models in the previous year. These comparisons are complicated by other design issues. In many cases automakers have introduced air bags coincidentally with other significant design changes. Thus many times results for models with and without air bags are not comparable due to substantial changes unrelated to occupant restraint systems. A superficial comparison of injury claim frequencies without detailed knowledge about other possible design changes of the vehicles isn't valid.
Furthermore, overall injury claim frequencies are very broad statistics that include all kinds of injuries — for example, injuries sustained in crashes in which air bags aren't even designed to work; injuries to body parts not protected by air bags; injuries of a comparatively minor nature, likes cuts and bruises; and injuries to occupants in seats where they're not protected by air bags. The presence of an air bag should not be expected to have any substantial effect on injury claim frequencies, which reflect all injuries regardless of severity. Such statistics are far too broad to assess air bag performance, as HLDI reports have repeatedly pointed out.
Air Bags Save Lives
When researchers use data that should be expected to reveal something about air bag effectiveness, the findings have been different. The latest research, for example, shows that 24 percent fewer driver deaths than expected occurred during 1985-92 in front and front-angle crashes of air bag-equipped cars, compared with similar cars equipped with lap/shoulder belts only. This saving of lives is over and above those already saved by safety belts in cars with air bags. Earlier HLDI studies have found moderate to severe injuries were 25 to 29 percent lower among drivers of 1990 model cars with air bags compared with drivers of 1990 cars with automatic safety belts. Hospital inpatient rates were 24 percent lower among drivers of cars with air bags.
Drivers of Cars with Air Bags Buckle Up
Hoffer speculates that injury claim frequencies may be higher in cars with air bags than in cars without air bags because drivers of air bag-equipped cars don't wear their safety belts. In fact studies by the Institute, the National Highway Traffic Safety Administration, and the University of North Carolina Highway Safety Research Center clearly document the contrary. An Institute survey of drivers of 1990-91 model air bag-equipped cars found that belt use is about the same as it is among drivers of late-model cars with manual belts only. Seventy-nine percent of drivers of cars with air bags were using belts, and 78 percent of drivers of otherwise comparable cars with manual belts only were using belts.
Hoffer is a long-time believer in the totally discredited theory of risk compensation. According to the risk compensation hypothesis, driving behavior is influenced by the risk of injury in a crash, and if that risk is reduced, it will lead to increases in hazardous driving behavior that will offset the benefits of the reduced injury risk. There is not one shred of empirical evidence to support this speculation. In fact, there is now abundant scientific evidence that risk compensation does not occur when car occupants have a reduced risk of injury in crashes.
The Institute remains wholly supportive of air bags and will continue to attempt to correct misinformation about this lifesaving device. In addition, the Institute has communicated with editors of publications in which Institute and HLDI data have been misused and has offered assistance in correcting misinformation.