A Washington Post headline proclaimed today that cyclist head injuries have increased in cities with bike-share systems, based on a study published in the American Journal of Public Health. But University of British Columbia public health professor Kay Ann Teschke is challenging that conclusion, pointing out that the data cited by the WaPo actually leads to the opposite conclusion: In cities with bike-share systems, head injuries and injuries of all kinds have gone down.
"The message that bike-share is increasing head injuries is not true," Teschke told Streetsblog. "The tone of the article suggests that head injuries go up. Really what is happening is that head injuries went down, non-head injuries went down -- but non-head injuries went down more."
The study was based on injury data from trauma center databases and registries in American and Canadian cities, collected over the same time period from both bike-share cities and control cities. A press release for the study said the "risk of head injury among cyclists increased 14 percent after implementation of bike-share programs in several major cities." But to put the finding in plainer language, what the researchers actually show is that head injuries as a proportion of overall cyclist injuries rose from 42 percent to 50 percent in five cities after the implementation of bike-share.
As for the overall safety of cyclists following the introduction of bike-share, Teschke says the data in the article actually show that total head injuries fell more in the five cities that implemented bike-share than in the control group. Head injuries just didn't fall as much as total injuries.
The AJPH article's authors make cautious assertions that their research might build the case for helmet requirements with bike-share. The Washington Post's Lenny Bernstein, meanwhile, wasn't cautious at all:
A few weeks ago, in honor of annual Bike to Work day, I asked a simple question about why those terrific bike share programs don’t provide helmets to riders. There were a lot of understandable reasons — hygiene, cost, liability — but one thing all the cities I checked seem to argue is that bike share programs are very safe, much safer than, say, cruising around on your own bicycle. Their evidence was anecdotal, based on the tiny number of reports of injuries to cyclists who have taken millions of bike share trips nationwide.
Well, it looks like they are wrong.
A look at the raw data doesn't support Bernstein's gloating at all.
In the cities that implemented bike-share, Teschke said, all injuries declined 28 percent, from 757 to 545. Head injuries declined 14 percent, from 319 to 273 per year. And moderate to severe head injuries also declined from 162 to 119.
Meanwhile, in the control cities that do not have bike-share, all injuries increased slightly from 932 to 953 per year -- 6 percent. Head injuries decreased slightly -- 4 percent -- from 356 to 342. And moderate to severe head injuries increased from 181 to 192. (All the information can be found in the above chart, but you need to divide the pre-implimentation data by two to control for the fact that that period was twice as long as the post-implementation period.)
Teschke attempted to notify Bernstein of the problem with the article in the comments of the story, and he was initially dismissive. He has since admitted in the comments that she is right, but had not adjusted his piece substantially at the time we published this post.
Teschke said the AJPH report could have just as easily focused on how bike-share is associated with lower injury rates -- both head injuries and overall injuries. Instead, the researchers, one of whom specializes in helmet research, chose to focus on this one piece of data -- proportion of head injuries -- to the exclusion of the larger picture: declining overall injuries. Teschke said she is planning to email the authors with her concerns and perhaps invite them to partner on a future study.
"I really feel badly that this wrong information is getting out there," Teschke said. "I don’t really think the results support their conclusion much."
