Time to explain why helmet laws don't work, again

Time to dust off all those compelling arguments for why mandatory helmet laws are counterproductive.  A bill in the Maryland House of Delegates would require all cyclists to wear helmets.  What's worse, the bill is cosponsored by a majority of the members of the Transportation Subcommittee of the Environmental Matters Committee, to which the bill has been referred.

I heard at an MDOT meeting a few months ago that a mandatory helmet law might be the price of fixing the 3-foot law, and almost every cyclist in the room said they would rather see both laws fail than both pass.  But some state officials (not from MDOT) were more sympathetic.  I was meaning to ask you for help in persuading some of those state officials, who advise departmental heads who, on occasion, have endorsed mandatory helmet legislation.

While I sometimes post articles on the Washcycle related to things I have been working on, in this case, I am soliciting input on a matter where most of what I know I have learned from you.

The obvious argument is that the requirement to wear a helmet will keep certain law-abiding citizens from riding a bike when they don't have their helmet.  That will kill bikeshare in Maryland--and it may prevent alot of other cycling.  The reduction in cycling will mean that some health and environmental benefits from cycling will be lost. 

What we need, is an estimate of the actual effect of a helmet law:  Presumably, it has little effect on people riding with hemlets anyway.  For those rides where a cyclist lacks a helmet today, what portion of those rides

• are unchanged--the cyclist ignores the law
• are cancelled due to lack of a helmet
• take place with a helmet as the law induces the cyclist to wear the helmet

The less obvious arguments, for which maybe someone has a good citation, concerns the circumstances in which a helmet has no net safety advantage.  If you know you will ride under some branches 2 inches above your head, you will be better off without the helmet.  Are there circumstances where someone would reasonably decide that this particular ride is safer without the helmet?  Otherwise, what is the incidence of accidents when helmet make things worse, compared to making things better?

The state official sitting next to me chuckled when I told him:  You would save more lives by requiring small children  to wear helmets when riding cars on interstate highways.  I have no data to back that up, it just seems likely that small children benefit from helmets so much more than adults that there are circumstances where children would benefit from helmets more than an adult cyclist.   Should I have suggested that children wear helmets before crossing the street?  Is there any research to make such a point on relative risk?

Finally, if they really want to help cycling safety, I wonder whether there are other equipment options that would do more good.  For example, requiring tail lights at night and enforcing the law on headlights?  Would raising the age where helmets are required from 16 to 18 be reasonable?  How about prohibiting pedestrians walking with their back to traffic at night from being entirely dressed in dark clothing?

Like it or not, Maryland is a state where people agree with the mandatory seatbelt and airbag laws. At first glance, mandatory helmet seem to be similar--and cyclists arguing against those laws sound like the libertarians that opposed seatbelt laws.  We need to learn how to explain to legislators and other state officials that actually, the helmet laws are very different.

(Jim Titus is a bicycle advocate from Prince Georges County)

Comments

[Early Man]

I think the most convincing argument for legislators is the detrimental economic impact helmet laws will have on the viability of bike sharing systems. A law that required drivers to supply their own safety equipment before renting a car would be seen as overly intrusive. Fortunately, for cars where the lack of safety equipment would be much more dire, this equipment is most effective when integrated into the design of the car. Helmets are only effective when fit to each specific rider and are commonly regarded as personal effects; i.e., privately owned articles for intitmate use by an individual.

[Chris Eatough, BikeArlington Program Manager]

Here is a summary of helmet law outcomes from around the world (lots of Australia and Canada).
Summary: Little or no reduction in head injuries. Dramatic drop in bicycle use. Net increase in relative risk of injury for cyclists.
http://www.onestreet.org/images/stories/pdf/Helmet_law_outcomes_summary.pdf

[twk]

Go to Copenhagenize and search on "helmet". There are some link to studies.

http://www.copenhagenize.com/search?q=helmet

Here is a good quote from one of the artivles:

Our society here - and elsewhere - has a simple and important choice:

What do we want for society as a whole?
A. More people in bike helmets?
B. More people on bikes?

You can't have both as common sense and the existing data will suggest.

For me B. is the obvious choice. The health and societal benefits are far greater when more people get onto bikes. A fall in illnesses like diabetes, heart disease and certain forms of cancer, a fall in obesity and a rise in productivity and life expectancy. Good for society.

[DE]

I think many people just assume that helmets make you safer--"it's just common sense"--but the data for this are iffy, showing improved safety in many instances but not in others. Why mandate something that has not conclusively been proven to improve safety and may actually reduce it in limited circumstances?

To me, the strongest argument comes down to this. Choose to wear one or not, but don't attempt to force people to use an item they don't believe to be universally effective.

Just as a FWIW on where I'm coming from, I wear one when mountain biking, in inclement weather, and when it's cold out, but rarely in the summer on the road. Others are free to disagree with my decision, but it IS a choice at least. I don't wish to be a law breaker, but I would be if it were mandated (bullet point #1).

[JG]

"a mandatory helmet law might be the price of fixing the 3-foot law"

What a strange statement ... it has the sound of a compromise or tradeoff, but I don't understand who the competing parties are.

Obviously with the 3-foot law the beneficiaries are cyclists, while drivers face a slight risk of additional fines.

But for the helmet laws ... are drivers supposed to benefit from that? If so, how? If not, who is supposed to be the beneficiary? If I put my conspiracy theory hat on, one way for drivers to perceive a benefit from it is, in fact, to reduce the number of cyclists on the road. In which case all of these studies saying cycling is reduced by a helmet law play directly into the goals of those proposing this rule.

[Crikey7]

I would caution against any argument that helmets don't increase safety, at least by some factor, on an individual basis. That argument will get us nowhere, not the least because it's almost certainly wrong. The other arguments are superior and don't get us sidetracked into a debate where the evidence is at best inconclusive for the argument you seek to make.

[NeilB]

Jim T, at the bottom of your post, you compared mandatory bicycle helmet laws to mandatory seat belt and airbag laws. A more apt comparison is that Maryland requires mandatory helmet use for motorcycle riders. We need to show the obvious difference between a motorcycle and a bicycle and between the two types of helmets and their effectiveness.

As other comments have mentioned, I think the focus should be on the usefulness of helmets in reducing injury (which is often overstated) vs. the effect that a mandatory helmet law would have on ridership.

Finally, for what it's worth, the current law (for 16 years old and younger) and the proposed law (for all bicyclists) both state that "This section shall be enforced by the issuance of a warning that informs the offender of the requirements of this section and provides educational materials about bicycle helmet use." Since there is no penalty, I wonder if it's correct to say that it's really mandatory.

[david]

Headlights and taillights at night ought to be law. As to the helmet. It should not be a violation that they can stop you for, but if you get hit and have a head injury seems only reasonable to say you contributed to your own injury. i.e. contributory negligence.

[NeilB]

One other thing: Given that there is a mandatory motocycle helmet law in Maryland, I think it is strange that the proposed bicycle helmet law specifically exempts moped riders. I don't see any rationale for that.

[me]

Funny to see the same arguments that were used against mandatory seatbelts - or even against requiring that seatbelts be included in cars at all, decades ago.

[jmarcusse]

Unfortunately this is a British study, but drivers leave less room when passing a bicyclist wearing a helmet. The article is behind a paywall but the abstract is still useful.

It may very well be that the safety benefit of wearing a helmet is outweighed by drivers increasing the chances of a collision.

http://www.sciencedirect.com/science/article/pii/S0001457506001540

[Greenbelt]

The revealing comment that the mandatory helmet law was the political tradeoff for the 3-foot rule makes it pretty clear that this is being pushed by drivers to get cyclists off the road.

[Mike]

The difference is that the data for seatbelts showed a dramatic decrease in serious injuries and fatalities with no negatives. For helmets, on the other hand, there is data showing that we don't have dramatic improvements in outcomes for helmet-wearing US cyclists vs cyclists in other countries with much higher levels of cycling and much lower levels of helmet use.

[twk]

@davis RE: contributory negligence.

I don't think contributory negligence should necessarily come into play. There are many cases where people get hit by a trucks and the helmet or not makes no difference.

As we all know the media likes to ask if the cyclist was wearing helmet and if not, immediately blames the victim regardless of the circumstances.

If this law passes we have a new layer of scofflawlessness to deal with.

If you really want to improve safety you need to have more cyclists (safety in numbers, there is data on that) and better infrastructure. This new law does neither.

[washcycle]

I wrote a separate post on this, but it is trapped on my home computer right now. But for me the opposition covers two areas.

1. It will reduce cycling, and we don't want to do that. The health and safety benefits of cycling far outweigh the risk of not wearing a helmet. And then we add in the reduced pollution, greater mobility and congestion reduction benefits and we come to the conclusion that we should do as little as possible to reduce cycling. And the cost of this initiative outweighs the benefits. This makes it different from motorcycling perhaps (though I oppose mandatory motorcycle helmet laws too).

2. Freedom. Being free means being able to do things that other people think is stupid - as long as it doesn't hurt anyone else. In the end, not wearing a helmet will only hurt the person who chooses not to do so. And so, people should be free to take personal risk, or else they aren't free at all.

[Elizabeth]

@NeilB: there is another law that was passed last year that makes helmets compulsory for people riding mopeds/scooters.

It's unclear to me whether the enforcement with a warning is the ONLY punishment, or if it would additionally be a misdemeanor like most other violations of vehicle laws under 27-101.

It also seems to add to the reasons for which police can make traffic stops, making easy targets of the members of society who can least afford helmets.

[SJE]

1. Helmets increase the risk of heat-related injury. Poorly ventilated helmets can cause riders to overheat their noggins, causing heat stroke. Even with well ventilated helmets, the sweat pouring down my face can obscure my vision, so the helmet has to come off.

2. Government should only restrict behavior if it is necessary for some specific goal, such as improved safety. Where is the evidence that helmets improve safety? Most bike fatalities would not have been stopped (or were not stopped) by helmet use. There are better ways to improve safety.

[NeilB]

Elizabeth: The general penalties for a misdemeanor are replaced by the specific provision of the helmet requirement in Section 21-1207.1 that the section shall be enforced by issuance of a warning. This is due to the fact that Section 21-1202 states that a person operating a bicycle has all the rights and duties of a driver of a vehicle except as provided in this subtitle (that is, Subtitle 12. Operation of Bicycles and Play Vehicles).

[Jonathan Krall]

The case against helmet laws:

- Because the health benefits of cycling outweigh the dangers by ten to one, the public policy imperative is to increase cycling first and foremost, even without any additional steps to increase safety.

- Helmet laws discourage bicycling use, especially for bikeshare, the use of which is often not planned (bikehare comes in very handy when mass transit fails). Studies typically show a decrease in cycling following adoption of a helmet law.

For me, those two points end it (especially the bikeshare issue--the helmet law seriously damaged the success of bikeshare in Melbourne). If one wants to get into safety and helmets anyway, here is some info:

- The safety problem for cyclists is collisions with cars, and the fatality rate for such collisions skyrockets above 20 mph. Helmets, however, are tested and designed for crashes at 12 mph. Helmets are a solution that does not address the real problem.

- Studies do not show efficacy of helmets. Specifically, because they effectively make the head bigger, they increase neck injuries, offsetting the decrease in head injuries (Elvik, Accident Analysis and Prevention, 2011). Studies do show correlations between helmet-wearing and safety, but those studies indicate that it is a matter of cautious people wearing helmets rather than the helmets themselves (City Cycling, eds. Pucher and Buehler, p 150).

[michael n]

Much of the interest in having cyclists wear helmets by legislators seems more belief-based than science-based. They believe, with no particular evidence, that a cyclist with a helmet rated as safe according to some standard, must contribute to the cyclist's safety in exactly the same way that a motorcyclist's helmet can contribute to his or her safety.

Intuitively that seems reasonable, but it would be better if there were good studies or good evidence, which there doesn't seem to be.

One aspect has to do with the types of serious accidents - most serious bicycle accidents involve cars or other vehicles and the imbalance of cyclist-vs-car usually means that a bicycle helmet isn't going to prevent the trauma that kills or seriously injures the cyclist.

Another is that bicycle helmets simply aren't that good. Of course they are better than nothing but if we really wanted bicycle safety, we should wear the same helmets as the motorcycle riders. Or at least something that is more sturdy than able to withstand a ball peen hammer at 13 mph (or whatever the standard is). Of course that line of reasoning - that we don't want to be required to wear helmets because they aren't very good - is a poor tactic.

But thinking it through - let's make a law that cyclists have to wear a helmet AND it has to be a much better (heavier, etc) helmet would have even more of the undesired effect of a helmet law with today's helmets - cycling would be less attractive and fewer people would do it.

It may be instructive to watch this video of Dutch cyclists - at about 5:30 the questions are about the reaction of Dutch cyclists to helmet laws. I realize we aren't trying to become the Netherlands, but it is interesting nevertheless.
http://youtu.be/Il1IGKaol_M

I particularly like the fellow who says that his friends who fall down when cycling are usually drunk and they may scrape their hands or their knees but they never bump their heads.

[JimT]

Thanks to all for your comments this morning. I finally have gotten to my lunch break so I shall quickly followup on a few of the comments where I quickly realized a need for additional clarification, either by me or a commenter.

First, I may have accidentally fueled more pessimism than intended about the legislative process, concerning the tie-in between the 3-foot law and helmet laws. People often say "I'll support your bill if you support mine," simply because they care about their bill more than your bill.

@Crickey and some others. I agree that overall helmets have a net safety benefit, and that denying such benefit would be unwise. I am trying to understand whether there is ever a case where a reasonable cyclist would choose not to wear a helmet, because if that is the case, then the logist for cyclist discretion is greater. Without more than I have so far, I would drop that line because I don't have any such examples. The accident-specific cases where a helmet does more harm than good are not sufficient to make that case, unless one has a way to know before-the-fact that such cases are more likely than usual. Those cases might still be useful to explain why the net benefits of helmets are less than one might assume.

@SJE: I think you have provided a case in point. At least one needs the discretion to not wear a helmet on a very hot day.

@all: The argument that the law discourages cycling which hampers safety is an independent argument which seems to have more support--but it is also counterintuitive.

@Early man and others. I think you are correct, and hopefully M-NCPPC will take a position. Yet some people make their endorsement decisions based on health and safety rather than economics. So an argument that appeals to them is needed, to help persuade their Secretary not to endorse the bill this time.

To all: The aticle Dl Robonson, "Head Injuries and Bicycle Helmet Laws", Accid Anal Priv, 28:463-75 (996) states that a mandatory helmet law for motor vehicle occupants would save 17 times as many people as a bike helmet law. But of course if it inconveniences 50 times as many people it might be viewed as less effective. Limiting it to children, however, would be more effective, because children and the elderly receive a disproportionate share of these head injuries. If you can send me a pdf of that article, please do.

@NeiB: Any more analysis on the comparison with motorcycle helmets?

@me: Are you sure these are the same arguments? I'd love to see the predictions that people would stop driving, or that car rental companies would go out of business with mandatory seatbelt laws.

@all: If anyone has a link to the short story of where the "85 percent of injuries can be prevented" please let me know.

@others--much good stuff here.

[JimT]

Oops. As usual, many typos from my fingers.

The article is by D.L. Robinson.

My penultimate comment was that I recall an analysis that showed the propogation of the myth that helmets are 80-85% efective in preventing head injuries, and provides a more accurate estimate.

[NeilB]

JimT: I don't have any specific analysis for motorcycle helmets. What I was saying is that I think instead of making a comparison between mandatory helmet laws and mandatory seat belt laws, a better comparison is between mandatory bicycle helmet laws and mandatory motorcycle helmet laws. And I'm saying that the two types of helmets and the vehicles themselves are sufficiently different that one shouldn't make the logical leap that if motorcycle helmets are required, bicycle helmets should also be required. Motorcycles are driven at much higher speeds than typical bicycle speeds, and motorcycle helmets are much more effective than bicycle helmets.

[Nicolle]

Have you seen this article? Perfect arguments & they cite people who have studied these questions.

"To Encourage Biking, Cities Lose the Helmets"
Published: September 29, 2012.

http://www.nytimes.com/2012/09/30/sunday-review/to-encourage-biking-cities-forget-about-helmets.html

[Jonathan Krall]

The "85 percent of deaths can be prevented" study (Dorsch et al, 1987) is described here: http://www.cyclehelmets.org/1136.html

This result was much criticized. Similar results have "not been seen in population-level research."(City Cycling, eds. Pucher and Buehler, p 149).

[Jonathan Krall]

And here are some numbers for Brisbane's bikeshare system, which launched with a 1060-bicycle setup similar to CaBi's initial setup. They got 80,000 rides in the first year, versus almost 1 million for CaBi in its first year (CaBi hit 1 million on day 366, its first anniversary).

http://en.wikipedia.org/wiki/Bicycle_sharing_system#Brisbane

[me]

Regarding "freedom" and not hurting anyone else:

If you want to also pass a law that says people who don't wear helmets who have head injuries aren't eligible for taxpayer-funded services like disability or welfare for their starving children whose daddy can no longer work, or collecting on insurance others pay into with premiums (or must pay higher premiums if they don't wear a helmet) then you'd have a point.

[me]

I was referring to mandatory seatbelts in cars as discouraging driving. Here's a brief reference to the seatbelt fear issue - which is actually supportive of the argument that helmet discourage cycling as well:

"As Ford stressed safety, GM continued using appealing ladies to advertise power under the hood. The buying public concluded that if Ford had to add so many safety features to its cars, they must have been more dangerous than other cars. Ford saw its sales plummet, with Chevrolet taking a convincing lead. That prompted Henry Ford II to say, "McNamara [Ford's President] is selling safety, but Chevrolet is selling cars." Ford's safety campaign had been a disaster; safety didn't sell. Ford shifted its ad campaign and did not offer seat belts as standard equipment in its '57 models."

http://www.secondchancegarage.com/public/seat-belt-historya.cfm

On seatbelt laws, I was talking about the "freedom" argument, not discouraging driving.

[washcycle]

JimT, you may be looking for this http://www.thewashcycle.com/2010/05/the-helmet-facts.html

[washcycle]

@me "If you want to also pass a law that says people who don't wear helmets..."

First of all, that's excessively punitive. We don't usually actively punish children for their parents mistakes. I doubt that is constitutional.

And second, if you want to decline insurance, survivor and disability benefits to those who die or are injured doing something risky then where is your list of risky behaviors that are more dangerous than helmetless cycling. Overeating is pretty risky. I'd say more risky. Also true of living a sedentary life. So they lose their benefits. Driving withuot a helmet is actually pretty risky, so it's out. As is walking without a helmet.

I think you see where that logic takes you.

[JimT]

@all: Thanks to an local advocate for sending me the pdf of the Robinson article. And I appreciate anyone who can send me a pdf of any key peer-reviewed journal articles that are behind a paywall.

If I somehow suck myself into testifying (which depends on the day of the week for the hearing) I probably will start by handing them a stack of research. This is the environmental matters committee, after all.

Back to work for me. As you probably all realize, my purpose here was mainly to stand on your shoulders rather than replough old ground. So if I do not respond to your comment, rest assured that probably means that you were very clear.

Thanks again!

Jim

[SJE]

Brisbane is not a good comparison to DC (much more spread out), but Melbourne is, and it shows the follow of helmet laws.

Melbourne is a large city built before motor cars, with a strong transit system and lots of people who live in or near the core. The weather is better than DC, and gas is much much more expensive.

Melbourne demanded helmet use. When they introduced a Cabi like system, they came with helmets for rent at kiosks like the bikes.

Not only Cabi, but all bikes are far less common in Melbourne than DC, according both to stat and from my visit there in December of 2011.

[SJE]

the FOLLY of helmet laws....

[contrarian]

If helmets were as effective as seatbelts it would be very hard to argue against requiring them. But they're not -- not by a long shot. There is legitimate doubt as to whether they increase rider safety at all. But most people assume they are highly effective -- they want them to be highly effective. This is why it is important to make an issue of their efficacy.

As to the argument that mandatory helmet laws reduce bike usage: for some people, that's a feature, not a bug. Many people feel that cyclists are coddled, and that bicycles don't belong on the roads. Until about 25 years ago, most bicycle-related laws were written with the purpose of keeping cyclists off the road -- "solving the bicycle problem" they called it. While that attitude has abated somewhat, it's still pretty widespread.

[David Patton]

Most cycling injuries are not head injuries, but to extremities - arms and legs.

Far more head injuries are suffered by motor vehicle drivers and passengers. If the societal goal is to prevent head injuries, then drivers and passengers should have to wear helmets. (And this is the rationale for requiring them to wear seat belts.)

On the other hand, if you want to add disincentives to cycling (make it less normal, less easy, less convenient), then by all means require helmets, registration, insurance. Even though those measures will never pay for themselves.

[Crikey7]

These are all well and god to debate internally. What we need, though, are arguments that work outside our group. And I see only two: (1) these laws significantly discourage bicycle use, which has a net negative effect on public health, and (2) incidents of serious head injuries or preventable fatalities measured against miles travelled, or trips taken, or other yardsticks, indicates that the risk is sufficiently low that a mandate is not warranted.

[Angelo Dolce]

To follow up on comments by David, twk and contrarian among others:

I think contributory negligence is a huge issue here. Other states with mandatory helmet (motorcycle and bicycle) and seat belt laws specifically exclude failure to comply from being considered contributory negligence. Even MD excludes failure to comply from reducing motorists' rights (MD Transp. Code section 22-412.3 seat belts, 21-1306.1 motorcycle helmets). I see no such protection for bicyclists in this bill or the existing bicyclist helmet law.

The bill makes riders to wear helmets at all times, specifically as safety equipment. Even when riders are hit by drunk motorist going 70mph in 30 mph zones (Philadelphia a few years ago), the news reports always mention helmets and quote the 85% figure. I think no helmet will be prima facie evidence of contributory negligence, even if it should be obvious helmets won't stop all injuries or deaths.

Laws in many other states are explicit that riding without a helmet is NOT contributory negligence and does not reduce the liability of a motorist otherwise at fault. MD specifies this in the seat belt law for motorists, and helmet law for motorcyclists. I am hard pressed to imagine that not a single person drafting or supporting this bill was aware of this or considered it an important issue; it has arisen in every discussion I've seen in other states.

It looks to me like by requiring helmet use by all bicyclists at all times, this bill makes riders without helmets ineligible for any compensation at all in collisions. This seems to be too big a benefit for motorists and insurance companies to be accidental.

Since it would be easy for this bill to address contributory questions in the bicyclist favor (as was done for motorists with seatbelts and motorcycle helmets), the current bill seems to have at least some supporters that are still trying to solve the "bicycle problem", to quote contrarian.

[UrbanEngineer]

Quite the discussion. Looks like all the major points got hit on. I'd just add that according to the NHTSA, 618 bicyclists were killed in the US in 2010. 598 of them were involved in collisions with motor vehicles. That's 96.7%. What do helmets do to prevent these collisions? Absolutely nothing.

[JimT]

@Angelo Dolce et al.
I am under the impression that until the opinion is issued for Coleman v. Soccer Association of Columbia, et al, legislators do not want to carve out any exceptions to contributory negligence. If a bill even has those words, someone might well say "Let's table this bill until the court decides the matter."

If the doctrine is struck down, there will be a serious effort to overrule the court, and all sorts of new exceptions will be proposed. If it is upheld it will be back to business as usual and the types of compromises you mention will become commonplace.

Hopefully the problem will not be as bad as you foresee. First, someone can already raise that issue--but how often does it come up? The defendant has the burden of proof on the causation issue, which is a pretty heavy burden--and almost certainly a question for the jury. Proving that the cyclist would have been fine had she worn a helmet is a very tough thing to prove.

Also, since the cyclist's negligence is long before the accident, the last clear chance rule should often save the case, or moot the need to even litigate the question.

[just another rider]

it would seem that the NHTSA might disagree with many posters here with their bullet-point publication: Bicycle helmet laws have proved effective in increasing bicycle helmet use.

The paper, despite the name, doesn't really seem to draw any conclusion, nevermind the one identified by the title with its masterful collection of bullet-points. In fact, the bullet points only dance around its topic, not really ever getting, pardon the pun, to the point.

The paper would seem to make it possible that Maryland would be the first to be listed as demanding a helmet on all riders, not just those underage.

[contrarian]

The NHTSA paper includes three "Key Facts":

* Bicycle helmets are 85- to 88-percent effective in mitigating head and brain injuries, making the use of helmets the single most effective way to reduce head injuries and fatalities resulting from bicycle crashes.

* Despite the fact that nearly 70 percent of all fatal bicycle crashes involve head injuries,
only about 20 to 25 percent of all bicyclists wear bicycle helmets.

* Every dollar spent on bicycle helmets saves society $30 in indirect medical costs and other costs.

They cite references but not sources.

Together these "facts" perpetuate the myth of the free-rider cyclist, selfishly imposing costs on others.

[JimT]

I found a copy of the 1989 Thompson et al. study which seems to be the source of the oft-repeated statistic about 85% inury reduction. The post that Washcycle cites in a short comment above, links to a critique--but we will need to get into the heart of the original paper, rather than the critique, to be in a position to really understand whether it is methodologically flawed or simply an old "data point" on a matter that ought to have been subject to ten studies since then.

The heart of that paper seems to be that 7% of the people with head injuries were wearing a helmet, while about 24% of a group with other injuries requiring hospitalization were wearing a helmet, and an different group of people (data from an insurance company) with any bike injury under a , no matter how slight, also had about 24% helmet usage.

The authors were really disturbed by the fact that only 2% of the children with head injuries had a helmet, while 6% with other injuries had a helmet, and 20% of the child cyclists with the health insurance company wore a helmet.

I think we will need to dust off Bayes theorem to make sense of the conclusions offered. (They do logit regressions but without more detail, we will never get behind that curtain.)

Can anyone walk through the probability inferences just from the basic summary data? The authors keep talking about an "odds ratio" but I would sure feel better if they just used Bayes Theorem, which at least forces you to admit what data you failed to get (i.e., they probably don't have p(helmet) or p(injury) and are just using the comparative studies in hopes that the ratio cancels out.

But if p(injury) is not stable accross the population.... And why would we expect that people with insuranbce have the same riding habits as those without, or ride in the same places, or on the same side of the street?

[Jonathan Krall]

@Jim,

One problem is that correlative studies show an effect, but population-level studies do not. The speculation is that cautious people are more likely to wear helmets. For example drunk cyclists in crashes rarely wear helmets (City Cycling, ed. Pucher and Buehler, p 150).

[JimT]

Hi Jonathan and others

Feel free to reiterate for me any studies I need to read. I worked my way through the Bayes Theorem stuff for Thompson et al., and at least for the two hospital groups I think that the "effectiveness" is 75%, as implied before they get into the regression analysis (about which I am skeptical).

By effectiveness, I mean that for the time period and region of Seattle studied, I think that it is reasonable to conclude that if you who wore a helmet, avoided colling with an automobile, got an additional 2 years of education, you would be 75% likely to sustain a head injury for the type of accident in which you would find yourself.

While the logit regression analysis purports to distinguish the effects of the various causal factors, I am dubious. Most important, the regression analysis attributes a greater effectiveness to the helmets than the difference in outcome from the data sets. That is not plausible, given that the set of head-injury victims were twice as likely to have been struck by an automobile, and had lower income and education, than those who did not sustain a head injury.

Finally, there is some likelihood that the sample construction in which one compares the data set with one type of an uinjury with the data set caaused by another type of injury causes biased estimates. The same analysis also shows that wearning a helmet makes one more likely to receive a non-head injury.

From my (brief) days as an economic modeler, I am dubious about multi-variate regression unless I see

UrbanEngineer, NHTSA report "Traffic Safety Facts, 2010 Data, Bicyclists and Other Cyclists" says that 24% of all cyclists killed had 0.01 g/dL Alcohol and 21% were above 0.08. Unfortunately, their charts then mix fatal crashes with drivers and cyclists ("alcohol involvment was reported...."). Not to negate your quote of the video, but it's anecdotal, rather than the statistics provided.

Contrarian pointed out the NHTSA reports aren't original research, though, and it may be the data represented probably has been picked through.

[UrbanEngineer]

I wasn't quoting any video or report. I got my data from the NHTSA FARS query data.