US bike hire schemes linked with greater risk of head injury - or are they?

American cities with bike sharing programmes similar to London’s Barclays Cycle Hire Scheme have seen an increase in head injuries as a proportion of bicycle-related injuries, according to a controversial new study. However, another researcher has pointed out that the actual numbers of head injuries in those cities went down.

Research from the University of Washington and Washington State University found that the risk that a bicycle-related injury involved a head injury increased 14 percent after bike-share schemes were begun in several major cities.

Of all bicycle-related injuries that occurred in bike-share cities (Boston, Miami Beach, Minneapolis, Washington, D.C., and Montreal, Quebec) during the study period, the proportion that were head injuries rose from 42 percent to 50 percent after bike-share program implementation. No such increase was found in cities without these programs.

Although the trauma-registry data for bicycle-related injuries for two years before and one year after bike programs began saw an increase in head injuries, it was not proven that these injuries occurred on a hire bike.

“Our results suggest that bike-share programs should place greater importance on providing helmets so riders can reap the health benefits of cycling without putting themselves at greater risk for injury,” said the research lead, Janessa Graves. 

In September, Seattle will be one of the first cities in the USA to offer helmet hire along with bikes. Helmets will cost $2 per day - a move that is forced by a local mandatory helmet law.
 
“It doesn’t take much effort to wear a helmet when you bike,” Graves said, “but doing so could make all the difference.”
 
But in the following days scorn was poured on the research by Kay Teschke, who studies city cycling at the University of British Columbia.

"When I actually looked at the data, I thought, oh my goodness, the injuries actually went down," she told CityLab. "In the bike-share cities, the total number of injuries went down, and the number of head injuries went down."

The article went on to point out that:

Graves and team reported that the proportion of head injuries as a share of total injuries increased in the bike-share cities after the programs began, going from roughly 42 percent to 50 percent.

Meanwhile, the proportion of head injuries to total injuries stayed statistically flat in the non-bike-share control cities, going from roughly 38 percent to 36 percent. 

From that, the researchers concluded that bike-share "is associated with increased odds that a person admitted for a bicycling-related injury would have a head injury." 

That's a very nuanced finding, with the key word in the report being proportion. It wasn't that head injuries increased in bike-share cities. It was that head injuries as a proportion of total injuries increased in bike-share cities, particularly in comparison with non-bike-share control cities.

"It seems critical to me, especially for people interested in bike-share, to report that injuries overall went down, including head injuries," says Teschke.

"That's really important. Especially because it is likely that cycling went up in those cities."