Highway Code revisions: helmet discussion

[pjclinch]

... although I had seen reference to some studies that at least gave me pause for thought in my reluctance to adopt helmet wearing.

But which question... should an individual put on a helmet for this trip, or should there be some sort of mandation? They're very different.

We are also more aware of the potential for unintended side effects of promotion, which don't necessarily impact on a personal decision to wear or not.

Yes. I think that's the same as I'm saying.

I think it probably is too!

[Jdsk]

... although I had seen reference to some studies that at least gave me pause for thought in my reluctance to adopt helmet wearing.

But which question... should an individual put on a helmet for this trip, or should there be some sort of mandation? They're very different.

We are also more aware of the potential for unintended side effects of promotion, which don't necessarily impact on a personal decision to wear or not.

Yes. I think that's the same as I'm saying.

I think it probably is too!

An agreement, that's even better than a consensus!

: - )

Jonathan

[pjclinch]

This implies, I think, that the evidential basis has weakened over the last decade or so. Would you say that that is true? I was assuming that the balance had not greatly changed, although I had seen reference to some studies that at least gave me pause for thought in my reluctance to adopt helmet wearing.

As upthread... it depends on the precise question that is being asked.

The evidence on helmets and head injuries has strengthened, but that cannot remove the limitations of the methodology in the published studies.

The evidence on possible confounders of that hasn't made much progress. That might have included any association of helmet wearing with risk taking, and some development of relevant subgroups.

It depends on the precise question being asked...
I think we've made progress on realising there are confounders (significantly for a lot of the work, boiling down to case/control gold-standard of effectively interchangeable randomly assigned and blinded cohorts not really existing, and for whole-population studies an obvious problem is they tell you about average cyclists that don't necessarily represent any real people.), but not so much on what to do about them.

The evidence for a major effect of risk compensation has weakened.

I'm not really convinced of that. As Stevek76 suggested it's not so much that the evidence for risk compensation has weakened, but it's a nightmare to systematically account for it and/or measure it (see above re. methodological problems).

The evidence for health benefits of quite small amounts of exercise has strengthened. This is crucial in promoting understanding of the issues and supporting the development of rational policy.

The evidence for the health/ harm ratio for cycling has strengthened. Ditto.

Aye, I'm with you there.

Pete.

[Jdsk]

The evidence for a major effect of risk compensation has weakened.

I'm not really convinced of that. As Stevek76 suggested it's not so much that the evidence for risk compensation has weakened, but it's a nightmare to systematically account for it and/or measure it (see above re. methodological problems).

As always I'd say that it's an effect (or collection of effects) that should be sought. But if we're using evidence-based methodology we should start in any particular setting by examining the evidence for it happening.

If there isn't any it might be because it isn't happening or because it is happening but the methods are underpowered to detect it.

Jonathan

[Jdsk]

This implies, I think, that the evidential basis has weakened over the last decade or so. Would you say that that is true? I was assuming that the balance had not greatly changed, although I had seen reference to some studies that at least gave me pause for thought in my reluctance to adopt helmet wearing.

The evidence on helmets and head injuries has strengthened, but that cannot remove the limitations of the methodology in the published studies.

The evidence on possible confounders of that hasn't made much progress. That might have included any association of helmet wearing with risk taking, and some development of relevant subgroups.

I think we've made progress on realising there are confounders (significantly for a lot of the work, boiling down to case/control gold-standard of effectively interchangeable randomly assigned and blinded cohorts not really existing, and for whole-population studies an obvious problem is they tell you about average cyclists that don't necessarily represent any real people.), but not so much on what to do about them.

I'd definitely agree if that said possible confounders (as would G and S). But I don't think that those confounders have received adequate study, which is why I said "hasn't made much progress".

Of course this overlaps with "risk compensation" because both are about behaviour and risk.

Jonathan

[Steady rider]

https://journals.sagepub.com/doi/10.117 ... 6211044353
back on page 1, I mention a USA report and provide some figures of risk levels, it appears the actual risk level is fairly small. In comparison it looks like the risk level for helmets increasing the accident rate could be much higher, as examples,
from page 1

Namiri et al data reports 78,070 head injuries for bicyclists and includes 11,812 for those with alcohol or drugs usage (this includes all head injuries, face included). Using an estimate of 25 -35 million aged 18 and over who cycle in the USA , it calculates at one head injury per 256 – 448 people or 0.39% - 0.22% per year for those who cycle.

compared with, The European Cycling Federation stated "… the evidence from Australia and New Zealand suggests that the wearing of helmets might even make cycling more dangerous."

Clarke and Gillham provide details from New Zealand of an increased accident risk from 31 to 69 per million hours cycle.
https://www.researchgate.net/publicatio ... jury_rates

[Jdsk]

https://journals.sagepub.com/doi/10.117 ... 6211044353
back on page 1, I mention a USA report and provide some figures of risk levels, it appears the actual risk level is fairly small. In comparison it looks like the risk level for helmets increasing the accident rate could be much higher, as examples,
from page 1

Namiri et al data reports 78,070 head injuries for bicyclists and includes 11,812 for those with alcohol or drugs usage (this includes all head injuries, face included). Using an estimate of 25 -35 million aged 18 and over who cycle in the USA , it calculates at one head injury per 256 – 448 people or 0.39% - 0.22% per year for those who cycle.

compared with, The European Cycling Federation stated "… the evidence from Australia and New Zealand suggests that the wearing of helmets might even make cycling more dangerous."

Clarke and Gillham provide details from New Zealand of an increased accident risk from 31 to 69 per million hours cycle.

Communicating the actual risk of injury is very important, and is an excellent question for consensus working.

Jonathan

PS: But I can't see the point of quoting from individual studies when systematic methods of review are available. What if other studies give different results?

PPS: I think that paper might be paywalled. In case others can't see the authors' conclusions here they are in full:

Conclusions
Intoxication is associated with increasingly severe injuries, hospital admissions, and head trauma in bicycle and e-scooter riders. The findings support awareness campaigns to educate riders about risky practices, improve non-auto infrastructure, and promote helmet usage.

[pjclinch]

The evidence for a major effect of risk compensation has weakened.

I'm not really convinced of that. As Stevek76 suggested it's not so much that the evidence for risk compensation has weakened, but it's a nightmare to systematically account for it and/or measure it (see above re. methodological problems).

As always I'd say that it's an effect (or collection of effects) that should be sought. But if we're using evidence-based methodology we should start in any particular setting by examining the evidence for it happening.

If there isn't any it might be because it isn't happening or because it is happening but the methods are underpowered to detect it.

Evidence of risk compensation in a system: there are humans and there is risk that can be varied (or be perceived to be varied) by behavioural adaptation. That's it!

It's completely fundamental to typical human behaviour. When things appear to get riskier we take more care. When things appear to be less risky we take less (and getting less risky may mean a change in the external situation or the participant getting more used to it or a mixture). The real trick is determining how much less/more and what the variation is between individuals, and that's a trick that nobody I've seen has yet come up with a good yardstick for.

Like a lot of psychology it's pretty messy stuff. But that's reality for you. If you're designing for people you have to take their range of behaviour, and the degree of its messiness, in to account.

Pete.

[mattheus]

What do we think about the latest report on air temperature affecting Heads-vs-Tails coin tosses?

The numbers look convincing at first, but I don't think they've considered thumb length.

[Steady rider]

But I can't see the point of quoting from individual studies when systematic methods of review are available. What if other studies give different results?

The USA study was on adults, provides one indication on a population basis. If other studies gave different results, may be the case.

Other studies may also be on a population basis, but in one country they may average 20 km per week per person and another 50 km per person, so the risk wants to be billion km perhaps. Hillman found life years gained v lost, factor of 20 for cycling. Finding sufficient studies to fit in with a systematic method may not be easy, data on cycling per state, province, country plus injury data to match, accounting for their level of provision for cycling and age grouping. Perhaps the best option is NZ, who have the data on time travelled by age group and injury data.
https://www.cycle-helmets.com/new-zeala ... users.html

[pjclinch]

What do we think about the latest report on air temperature affecting Heads-vs-Tails coin tosses?

The numbers look convincing at first, but I don't think they've considered thumb length.

This underlines that whatever the literature says it shouldn't directly inform policy, but it should simply suggest changes in policy that are then confirmed (or not) by tests of change, and then if they are seen to work put them in to policy.
As far as I can tell DfT has never done a test of change on helmet promotion, they just decided it needed done and did it. And after the Highway Code introduced the current Rule 59 nobody's obviously got any data to show what the effect was: it wasn't dome properly in a way that could be tested.

So rather than worry about the air temperature and thumb length we notice that despite much debate in The Journal Of Rotational Coin Landing Science, we still get about 50/50 heads/tails and so we don't introduce new advice about using coin tossing in probability lessons.

For a proper review asking "how come this advice is in here?", if (as I suspect) the answer is "oh, we just felt the wind of change from the academic research" then that's really not good enough. They should see what effect a test of change has, and according to that test move forwards (or not).
"But my long-thumbed coin-flippers will make all the difference according to Smith & Jones '2021!"
"So show us"
(1000 coin tosses later, 503 to 497)
"3 more, that proves it!"

This wouldn't get you very far in quality improvement science, but it's apparently fine in road safety...

Pete.

[thirdcrank]

The point seems to remain that the most scientifically pure debate is unlikely to make any difference to official attitudes in general or helmet advice in the HC in particular. I fancy the only thing which might alter this would be the unlikely event of a government being genuinely committed to a policy to promote cycling deciding to scrap every barrier to achieving that policy, when ditching helmet advice would be an obvious starter. We would, of course, need some form of protective headgear and perhaps capes, to save us from the manure of the airborne pigs

[Stevek76]

The evidence for a major effect of risk compensation has weakened.

I'm not really convinced of that. As Stevek76 suggested it's not so much that the evidence for risk compensation has weakened, but it's a nightmare to systematically account for it and/or measure it (see above re. methodological problems).

Quite, I'm not sure how a collection of studies that fundamentally misunderstand the concept they're supposed to be looking for can count as weakening evidence. It's like trying to dismiss supermassive black holes by pointing your telescopes at the planets in this system and not finding any.

The review also falsely categorises the one study that's perhaps the most useful, that by Phillips et al in 2011, on the basis the it shows the effect in the 'wrong direction'. It doesn't, the cyclists who normally wore a helmet and had it removed slowed down in response, exactly as we'd expect. That those who did not normally wear one didn't respond to wearing one is very likely just because the cycling task involved was trivial, not because the effect did not exist.

As the Adams/Hillman dissent posted earlier notes, helmets strongly fit all four of hedlunds criteria for when risk compensation will be strongest.

[Jdsk]

The evidence for a major effect of risk compensation has weakened.

I'm not really convinced of that. As Stevek76 suggested it's not so much that the evidence for risk compensation has weakened, but it's a nightmare to systematically account for it and/or measure it (see above re. methodological problems).

Quite, I'm not sure how a collection of studies that fundamentally misunderstand the concept they're supposed to be looking for can count as weakening evidence. It's like trying to dismiss supermassive black holes by pointing your telescopes at the planets in this system and not finding any.

The review also falsely categorises the one study that's perhaps the most useful, that by Phillips et al in 2011, on the basis the it shows the effect in the 'wrong direction'. It doesn't, the cyclists who normally wore a helmet and had it removed slowed down in response, exactly as we'd expect. That those who did not normally wear one didn't respond to wearing one is very likely just because the cycling task involved was trivial, not because the effect did not exist.

As the Adams/Hillman dissent posted earlier notes, helmets strongly fit all four of hedlunds criteria for when risk compensation will be strongest.

If that's a reference to the idea that eg the SRs on helmets and injuries are the best available source of evidence on risk compensation then I agree.

But that wasn't what I was referring to in the weakening of evidence. It was this sort of thing:

"Bicycle helmets and risky behaviour: A systematic review"
https://www.sciencedirect.com/science/a ... 7818305941
Might be paywalled, so abstract in full:
A long-standing argument against bicycle helmet use is the risk compensation hypothesis, i.e., increased feelings of safety caused by wearing a helmet results in cyclists exhibiting more risky behaviour. However, past studies have found helmet wearing is not associated with risky behaviour, e.g., committing a traffic violation was positively associated with a lower frequency of helmet use. There is a lack of consensus in the research literature regarding bicycle helmet use and the risk compensation hypothesis, although this gap in knowledge was identified in the early 2000s. This is the first study to carry out a systematic review of the literature to assess whether helmet wearing is associated with risky behaviour. Two study authors systematically searched the peer-reviewed literature using five research databases (EMBASE, MEDLINE, COMPENDEX, SCOPUS, and WEB OF SCIENCE) and identified 141 unique articles and four articles from other sources. Twenty-three articles met inclusion criteria and their findings were summarised. Eighteen studies found no supportive evidence helmet use was positively associated with risky behaviour, while three studies provided mixed findings, i.e., results for and against the hypothesis. For many of these studies, bicycle helmet wearing was associated with safer cycling behaviour. Only two studies conducted from the same research lab provided evidence to support the risk compensation hypothesis. In sum, this systematic review found little to no support for the hypothesis bicycle helmet use is associated with engaging in risky behaviour.

And across other activities:

"Is risk compensation threatening public health in the covid-19 pandemic?"
https://www.bmj.com/content/370/bmj.m2913
which concludes:

What systematic reviews conclude about risk compensation
Helmet wearing
“In sum, this systematic review found little to no support for the hypothesis bicycle helmet use is associated with engaging in risky behaviour”15
“The use of safety helmets also does not appear to increase the risk of compensation behavior as compared to non-helmeted participants in skiing and snowboarding”16
Pre-exposure prophylaxis to prevent HIV infection
“One concern about PrEP [pre-exposure prophylaxis] is that its use may lead to persons at risk of HIV acquisition not using condoms or engaging in other behaviors that could increase their risk of STIs [sexually transmitted infections] (ie, behavioral risk compensation). In meta-analyses of the studies reviewed by the USPSTF [US Preventive Services Task Force], there were no differences between PrEP and placebo or no PrEP in risk of syphilis (4 trials; RR, 1.08 [95% CI, 0.98 to 1.18]), gonorrhea (5 trials; RR, 1.07 [0.82 to 1.39]), chlamydia (5 trials; RR, 0.97 [0.80 to 1.18]), or combined bacterial STIs (2 trials; RR, 1.14 [0.97 to 1.34]).”17
Circumcision to prevent HIV infection
“To date, there is little evidence from the few studies available of either unsafe practices or reported increases in risky behaviour”18
HPV vaccination to prevent cervical cancer
“The consistent, replicated evidence found across the 20 studies examined in this systematic review provides a strong body of evidence refuting that there is an association between HPV [human papillomavirus] vaccination and risky sexual behaviour”19

(The systematic review in the first statement of the second pair is the same as the one to which I've linked above.)

Jonathan

[mjr]

Equating traffic violations to risky behaviour as in "Bicycle helmets and risky behaviour: A systematic review" seems dodgy to me. Many safety improvements — including advanced stop lines, "except cycles" plates (and associated legal relaxations) and the Netherlands cycleway network — are at least partly due to massive breaking of motorist-centred laws by safety-concerned cyclists.