Helmets: Are bad stats leading to bad bills?

California state senator Carol Liu introduced an all-ages bicycle helmet bill yesterday, much to the dismay of many people who know a thing or two about helmet legislation. The early betting has the bill dying quickly in committee or elsewhere, although in a sense it might be productive to have a full and lively hearing about the merits of bicycle helmets. Some of the dismal, even disastrous, examples from places like Australia and New Zealand — where helmet legislation has apparently had no safety effect while also reducing cycling significantly — might kill these ideas for years to come.

Senator Liu’s press release included this statistical “gem” taken from a report by the National Conference of State Legislatures (NCSL): “Ninety-one percent of bicyclists killed in 2009 reportedly were not wearing helmets.” Since she mentioned it, Senator Liu is apparently relying in some part on this number to make her case. Where does it come from? Does it hold up to scrutiny? Does it reflect the California experience?

The underlying NCSL report doesn’t mention sources, but it’s a pretty safe bet that its numbers are coming from FARS, the federal Fatality Analysis Reporting System. FARS, in turn, gets its data directly from state highway data collection systems, which are implemented at the local law enforcement level. In California, the Statewide Integrated Traffic Records System (SWITRS) plays that role, and its data is open to all comers — including me, as it happens.

Over the past few weeks, I’ve been toying with SWITRS data, trying to understand its structure, and looking into what it might reveal about our roads. I’ve only gotten my feet wet with it so far, and I’ve much to learn, but from what I’ve seen, Liu’s “ninety-one percent” number is problematic. Take the year 2009, the year she singles out for mention. FARS shows 628 total cyclists killed in the U.S. that year. SWITRS tells me that 107 California cyclists were killed in the same year; presumably, those 107 are included in the 628 total. How many of those killed California cyclists were wearing helmets? SWITRS tells me there were twenty-two cyclists wearing helmets, sixty-seven who weren’t, and eighteen unknowns. In other words, in California sixty-three percent didn’t wear helmets — not ninety-one percent, as the nationwide number suggests — twenty-one percent wore them, and for seventeen percent of cycling fatalities we have no data.

My point might be small, but it should be in the mix nonetheless: Senator Liu implies that only eight percent of killed cyclists are wearing helmets, but in California that’s just not the case. More than double the cyclists are wearing them, and even more might be, if we knew more about those many unknowns. The hard facts? Lots of Californian cyclists are being killed despite their helmets, just as other studies show. We need to spend time confronting the real factors, like bad road design, high speed limits, and poor cycling infrastructure if we expect to make a real dent in fatalities.

Where does FARS get that huge ninety-one percent number? I’m not sure yet, but it sure looks suspiciously like they are grouping the unknowns in with the nos. That is a big no-no!

Just for completeness, I went back and extracted the numbers for all the years for which we have full SWITRS data (2001-2012):

Year	No Helmet	Helmet	Unknown			No helmet	Helmet	Unknown
2001	76	17	23	116		66%	15%	20%
2002	78	22	15	115		68%	19%	13%
2003	81	27	18	126		64%	21%	14%
2004	74	27	22	123		60%	22%	18%
2005	75	20	37	132		57%	15%	28%
2006	100	34	21	155		65%	22%	14%
2007	76	25	23	124		61%	20%	19%
2008	73	30	27	130		56%	23%	21%
2009	67	22	18	107		63%	21%	17%
2010	67	24	20	111		60%	22%	18%
2011	81	33	26	140		58%	24%	19%
2012	77	49	20	146		53%	34%	14%

As far as I can see, never in the past twelve years of data has any year approached Senator Liu’s number. Whatever comes of Senator Liu’s legistration, we should make sure that incomplete data don’t lead to bad statistics used to justify bad policy enshrined in unhelpful laws.

The Social Cost

In my memory, he was a reed-thin, almost delicate man, with curly hair and a slightly exasperated demeanor. He was obviously intelligent, and his lectures in my philosophy of law class were always rich in detail and balance. He tackled the big subjects — the death penalty, for instance — with the same even-handedness as others, always probing, always neutral. I was a little surprised when he revealed his love for motorcycle riding, and even more surprised when he expressed such disdain for California’s mandatory motorcycle helmet legislation, which was then on the books but not yet in effect. His opinion still sticks with me today: “I would rather not ride,” he said, “than ride with a helmet.” I’m a little sorry that I didn’t keep up with him after I left school; I don’t know whether he quit riding the following year or two when motorcycle helmets became obligatory for everyone. What I do still find interesting, though, is that the same arguments we tackled then in class over motorcycle helmets are now, nearly twenty years later, being broached yet again, this time in a huge war of words over bicycle helmets.

Elly Blue’s recent Grist article on bicycle helmets sets out the major combatants, with some particular focus on Copenhagenize.com‘s Mikael Colville-Andersen, calling him “the face of the anti-helmet movement.” I’m not sure that this designation is entirely accurate, for it ignores his many antecedents and philosophical compatriots. It also puts him in the uncomfortable position of being an “expert” on bicycle helmets, a moniker that he probably doesn’t want or deserve. Imagine the decision matrix of alien, asked to make a choice about helmet wearing, with the only inputs being these two TEDx videos about helmets, posted only a few days apart:

If I were that alien, presumably a bit risk averse and self-preservationist, I’d probably err on the side of caution, and go with Dr. Gergens’ advice to wear a helmet, even if she seems a bit smarmy and overbearing. She’s an expert on the brain; he’s a photographer who takes many photos of well-dressed women riding bicycles. Her qualifications go far beyond Colville-Andersen’s I-read-a-few-papers “research” résumé.

Any discussion over helmets really comes down to two questions, both related but with different arguments underpinning them:

► Should I, as an individual, wear a helmet?

► Should we, as a public policy matter, make helmet wearing mandatory?

These are yes-no questions, and their possible answers are straightforward:

Personal Choice	Public Policy
I wear a helmet	I want mandatory legislation
I don’t wear a helmet	I don’t want mandatory legislation

The American cyclists I’ve met and read tend to have the ideological viewpoint represented in red: they (mostly) wear helmets while riding but think mandatory legislation isn’t necessary. I share the same viewpoint. I wear a helmet because I feel safer. This is my choice. But the broader issue of whether we ought to require everyone to wear them requires a far different calculus. Public policy is not about personal decisions writ large, but about the (too often negative) impact of collective decisions writ small.

Part of the problem may be that it’s difficult to tease apart motorcycle helmet arguments from bicycle helmet arguments. It’s tempting, of course, to equate the two, given that they both involve two-wheeled machines and both involve helmets, but there are real and substantial differences in their application. For those who haven’t seen them, the best anti-and-pro mandatory motorcycle helmet arguments can perhaps be summarized in two lines:

► Anti: The state has no compelling interest in making helmets mandatory because the decision to wear them or not affects no one else.

versus

► Pro: The state has a compelling interest in mandating helmets because the “collective social costs” (direct medical, reduced productivity, emotional distress) to the society are higher when unhelmeted motorcyclists get into crashes.

Given the U.S. Constitutional principle of substantive due process of law, which requires (among other goals) that legislation be “narrowly targeted” at a “compelling” state interest, the cost argument has done all or most of the work of finding a state interest. Without that, it becomes more difficult to show why the state has any interest in interfering in the private choices of individuals (the anti argument), even if you happen to think helmet-wearing is generally a good idea. It’s probably a good idea to wear shoes while walking on concrete, too, but passing a law to mandate shoe-wearing probably doesn’t make sense.

Whatever its shortcomings, the cost argument probably applies to the bicycle helmet debate exactly opposite to the way it is generally applied to motorcycle helmets; that is, requiring bicycle helmets has a higher social cost than not requiring them. If we accept that there are large societal benefits to cycling — which seems to be universally acknowledged even by people temperamentally skeptical of cycling — this conclusion depends almost entirely on the large question of whether mandatory helmet legislation tends to reduce ridership. The studies on this point are inconclusive, but generally tilt towards answering yes.

Studies aside, helmets must have a negative impact on cycling for the simple reason that they complicate the decision to ride. Helmets have to be purchased, carried, and worn. They are non-integral to the act of cycling, unlike, say, the way an arrow is integral to the act of archery. If they’re lost, they have to be replaced. I could go on…

In the motorcycle domain, there was a collective shrug over the (possible) departure of helmet-hating riders. The government didn’t really care whether we had fewer motorcycles on the road. The public good wasn’t enhanced or diminished by their absence. Motorcycles may reduce congestion, but by some metrics, they can increase (!) pollution, and they do nothing for public health. By contrast, the benefits of cycling mean that reduced ridership would have a negative cost.

Fortunately, at the moment I don’t know of any serious proposals to make helmets mandatory, at least not in California. Los Angeles mayor Antonio Villaraigosa found himself booed when he mentioned such a proposal earlier this year. Maybe that reaction, and more like it, will keep it off the agenda for now … and for good.