Re: Helmet efficacy test

On 3/26/2025 11:47 AM, Frank Krygowski wrote:

On 3/26/2025 10:16 AM, Zen Cycle wrote:

On 3/25/2025 10:24 PM, Frank Krygowski wrote:

On 3/25/2025 5:02 PM, cyclintom wrote:

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How would you propose that a helmet cause a head injury? You could argue that the foam helmets are heavy and might increase your chances of hitting your head but the Wavecel helmets are light. Helmets don't interfere with vision on a normal road bike.

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There's data out there indicating that people wearing helmets do crash more (and show up in ER more) than people without helmets.

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Irrelevant, even if it were true. Statistical analysis on injuries with vs sans helmets take that into account.

 Nope. Here's why:
 The typical "case-control" study design - that is, counting head injuries (usually) or brain injuries in those presenting to ER, is built on the assumption that the sample presenting to ER is representative of the cylcling population as a whole. There's a significant amount of data showing that's not the case. Specifically, people wearing helmets present to ER more than the general cycling population.

I've already presented several studies that show more parity. You've been reading old literature.

 The easiest example to find is the 1989 Thompson & Rivara paper.

Yup, a 35 year old paper....that's currently valid alright, no one has done any substantive work in the area in the last 35 years...<eyeroll>

That team of doctors was all in on helmet promotion before they published their "case-control" study claiming 85% protection. They had just completed street surveys of the study area that found ~3% of cyclists were wearing helmets. But the cyclists presenting to ER had 21% wearing helmets. IOW, a person wearing a helmet was seven times more likely to show up in ER.
 Why would that be? There are various possibilities. One might be that the most nervous people would be the first to cave in to helmet fear mongering, and when they felt a head bump they thought "Omigosh, I might die!" and went to ER just to be sure. Another might be that helmeted people might suffer more head (or really, helmet) strikes with the ground just because the helmet is bigger than the head. (Evolution, like of reflexes and neck muscles, etc. tends to be efficient, i.e. nothing extra.) It might be that the people in helmets had better insurance coverage and didn't fear ER expense.

In 1989, that was likely the case.

 There were other differences between the "cases" and "controls," as well as between both groups and the general population - as explained here:
https://www.cyclehelmets.org/1131.html  and that is generally the case. Another study by a Dr. Crocker of Austin, TX was performed specifically to promote the idea of an all-ages mandatory helmet law (MHL). Crocker's study failed to find significant benefit from helmets, largely because he included a confounding factor almost always missed: Alchohol consumption. He found that drinking then riding significantly increased risk of brain injury, but riding sober without a helmet did not have significantly more risk than riding with a helmet. This is important, because (almost?) all other pro-helmet studies have not recorded blood alcohol content, and there's no way to retroactively know which of the injured no-helmet folks were tipsy.

Again, try to keep current:
https://pmc.ncbi.nlm.nih.gov/articles/PMC6747631/
"There was an association between alcohol intoxication and the failure to wear a cycle helmet (p<0.001). However, there was no correlation between crude mortality and alcohol consumption (3.5% vs 3.2% NS); this was true for those wearing a helmet (2.4% vs 1.8%) at the point of injury and those not (6% vs 3.8%)"

 

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(No, it's not

because those without helmets didn't survive, as some have claimed.)
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While not a direct mechanical cause if injuries, some studies - and many, many posted discussion remarks - indicate that people wearing helmets are indulging in "risk compensation" meaning "Hey, I'm wearing a helmet do I can take more risks." (I did that today, but I'll probably wait until tomorrow to post about it.) We've had people post here that they would never do the risky mountain biking they do without the helmet. We've had people say "I would never ride that busy road without a helmet."
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Risk compensation is probably near-universal with lots of "safety" devices. It's not inappropriate as long as the increase in risk is commesurate with the increase in protection.

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Again irrelevant. The Moral Hazard argument has a place, but it isn't in the discussion of whether helmets are protective or not.

 If you're restricting discussion to mechanical effectiveness, you're correct.

Thank you

If you're allowing discussion on overall reduction in brain injury due to widespread helmet use, you're wrong. If a person takes additional risks because of overestimating his invulnerability, he's likely to pay for the indiscretion. And almost all helmet promotion is intended to trigger widespread use in hopes of reducing total injury rates or counts.

And it does, even with "risk adjusted" studies. From the above study:
"There was an increased crude 30-day mortality in the group not wearing a cycle helmet 5.6% (4.8%–6.6%) versus helmeted cyclists 1.8% (1.4%–2.2%) (p<0.001); corresponding risk adjusted excess survival rates (W scores)22 were 1.1 (−0.1 to 2.2) and 2.4 (1.3–3.6), respectively."

Trouble is, the protection from a bike helmet is far, far less than people are led to believe. Look up the standardization test.

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"led to believe" by what metric? I've never seen any literature claiming a helmet _prevents_ serious head trauma.

 WHAT???

No helmet manufacturer or helmet advocacy group claims helmets _prevent_ serious head trauma. They _can_ reduce severity, not prevent it.

 

Oh, and about helmets mechanically causing injury? Curiosity about that surged once it became clear that helmeted cyclists seemed to be over represented in concussion counts.
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Well, since the helmet certification standard was established (essentially less than 300gs linear deceleration in a 14 mph impact), it became known that linear deceleration was far less of a problem than rotational acceleration. Twisting the head and brain caused far more brain injury than smacking them. But a helmet protrudes at least an inch from the head, providing a longer lever arm for glancing blows, potentially worsening rotational acceleration. (Note that a bare head's slippery hair and very loose scalp are probably evolutionary tricks to reduce that hazard. The helmet makes those ineffective.)

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a specious argument with no scientific substantiation.

 What part did you not understand?

I understood all of it. What I'm stating is that you have no data to support the that helmets "provide a longer lever arm and thus can cause more injury" claim. Every study I've link states the exact opposite.

 

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