Tuesday, August 08, 2006

Non Sequitur Alert, Lawnmower Injuries Edition

A study from the Center for Injury Research and Policy at the Columbus Children's Research Institute shows that about 9400 children and teens are injured in lawnmower accidents each year (UPI report; CCRI website).

According to one of the study’s authors, “We found that the annual number of lawn mower-related injuries remained relatively consistent during the 15-year period studied, which demonstrates that current injury prevention strategies are inadequate.” There follows a list of recommended changes to produce safety standards.

Two problems. First, if the annual number of lawnmower injuries has remained constant for 15 years, then the annual rate must have fallen (because the population has risen). So arguably, we’ve seen an improvement in lawnmower injury prevention – either from better safety technology or from fewer children mowing the lawn. Or maybe the author simply misspoke, and it was actually the rate that remained constant.

Second, even if the rate were constant, how would that figure show injury prevention strategies are inadequate? Complete non sequitur. We cannot simply compare the number to zero; one-hundred percent safety is simply not an option, in life or in lawn-mowing. To judge the claim, we’d need to know much more than the raw number (9400 injuries per year!). We’d need to know the actual rate of injury, how it compares to other sources of injury, the costliness of better safety measures, and so on.

Neither the UPI article nor the CCRI website provides any perspective, so I will. The current U.S. population aged 0-19 is about 81 million. So 9400 injuries comes to a rate of about 11.6 per 100,000. For comparison, the rate of drowning or near-drowning for the same age range is 6.7 per 100,000; non-fatal inhalation or suffocation, 25.26 per 100,000; non-fatal dog bites, 193 per 100,000; non-fatal poisoning, 221 per 100,000. (All data from the immensely useful WISQARS website.)

Taken in context, then, a rate of 11.6 per 100,000 doesn’t seem especially large. Does the frequency of dog bites indicate that our dog-containment policies are inadequate? Or does it say more about the frequency with which kids interact with dogs? Still, it’s possible that lawnmower injuries are especially responsive to relatively low-cost alterations in behavior or technology, so the authors might be right to recommend change. The public summary of the research just doesn’t provide any reason to think so. I hope the complete study does a better job.

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