| Fallacy | Used by: | Example |
| Ad-Hominem
Ad Hominem arguments seek to discredit a claim by attacking the person making the claim. This is one of the most common forms of fallacious argument on Usenet. |
Ad-Hominem Circumstantial
| both, but maybe sceptics more often | David Coulthard is bound to say helmets are good, he has an interest in selling them.
CTC are opposed to helmet laws because they just want to get more members |
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| promoters | You say that, but I know you wear a helmet sometimes. |
Personal Attack (basic Ad-Hominem)
| both | Too unedifying to mention... |
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| promoters | Bill Zaumen continually referred to Tom Kunich having been arrested for striking his partner, and asserted on this basis that his arguments were not credible.
<a href="Scharf">Steven Scharf</a> says: "I used to respond to the anti-helmet zealots on Usenet. Then I realized how hopeless it was to attempt to educate them"; he seeks to portray sceptics as zealots, rather than people who have come to be suspicious of aggressive helmet promotion. |
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| both, but mainly sceptics | Sceptics are prone to poking fun at those whose defence of their point of view is less than erudite. Stop it, lads, it's not big and it's not clever. Well, not very clever anyway. |
| Ambiguity
Language is used unclearly, whether deliberately or not. |
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| promoters | 100,000 children are treated in hospital in the UK every year for cycling-related injuries
Head injury is the leading source of permanent disability and death in the 12-16 age group
See how two definitions of injury are used? In the first, injury means anything serious enough to need treatment at hospital (actually hospital, minor injury unit or GP clinic, but let's not quibble). In the second it is massive trauma leading to permanent intellectual disablement or death. This is extremely common in pro-helmet literature. I have never seen a pro-helmet document which made it clear that the brain injuries prevented by helmets are usually simple concussions with no lasting consequences. |
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| probably both | As often as not this really comes down to equivocation, or failure to define particular terms such as "head injury" or "serious injury". The term serious injury is largely subjective among a lay readership. |
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| both | Sceptics will emphasis the serious connotations raised by the term brain injury when promoters say helmets prevent brain injuries
Promoters will castigate sceptics for saying that helmets don't prevent injury when sceptics say they don't prevent injuries of genuine concern. |
| Appeals to Motives |
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| both | Not common, but occasionally used as for example "John Franklin is sceptical of the arguments for compulsion".
Also applies to celebrity endorsements of the type BHIT use in their literature. |
Appeal to Anonymous Authority
| mainly promoters | "Doctors agree" is the classic example of appeal to anonymous authority. This has been quoted in terms of "a leading brain specialist I know says..." - although to be fair the poster did then go and talk to the man and found that his view was a good deal less emphatic; they were then big enough to come back and admit it. |
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| promoters | Used as an argument for compulsion, as in: "They're wimps. Everyone else has brought this law in. Australia, America..." - Angela Lee. |
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| promoters | Reference to the number of doctors supporting helmet use and compulsion is an appeal to belief. |
Appeal to Common Practice
| both | Most cyclists don't wear helmets.
Most mountain bikers do. |
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| promoters | "I don't want to end up in a hospital Accident and Emergency department with a head injury. I'd probably never be able to drive a racing car again if I did and that's not a risk I'm prepared to take." - David Coulthard, in a BHIT leaflet.
It is important to distinguish between this and adverse consequences for which there is reasonable evidence, such as the idea that helmet promotion might deter cycling by giving a false perception of danger. |
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| promoters | Think of the children... Shroud-waving, as seen in <a href="Annetts">the Annetts case</a> is an example of appeal to emotion. |
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| promoters, occasionally sceptics | Any shroud-waving, any mention of serious or fatal injury, any mention of permanent disability or intellectual impairment. These are extremely rare outcomes, and anyway unlikely to be preventable by helmets.
Sceptics might note that the Government says it is resisting a helmet law at present solely because wearing rates are too low; therefore every rider wearing a helmet is making compulsion more likely. Accurate, but relatively unlikely at present, hence an appeal to fear. |
Appeal to Fear: Slippery Slope
| sceptics | As an argument against promotion - "what next?" and compulsion for certain groups or individuals (who next?).
Can be valid if, as per the example of compulsion deterred by wearing rates, there is credible evidence to support the proposed escalation of effect. |
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| both | But surely you are too smart to be taken in by such an argument. |
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| both, mainly promoters | A counter to the argument that we've been cycling for 125 years (not all of us, obviously) without dying out; helmets are "new".
Touting some new piece of evidence as supplanting all previous evidence: Ontario's experience (cycling not deterred) trumps Australia and New Zealand's massive drops in cycling, and let's not mention the fact that the Ontario law was never enforced, wearing rates are now back down to pre-law levels. |
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| promoters | Shroud-waving |
Appeal to Popularity'' (Ad Populum)
| both, mainly promoters | Promoters point to the large number of interventionist medics who support helmet use, promotion and often compulsion.
Sceptics point to the fact that there is a consensus among informed cyclists against compulsion. |
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| sceptics | We made a big fuss about Eric Martlew and Angela Lee being overweight non-cyclists. |
Appeal to Ridicule / Reductio ad Absurdam
| both, mainly sceptics | Sceptics ridicule the inflated claims of promoters and thereby obscure what evidence there is of efficacy lower down the severity scale; reference is often made to being hit by a juggernaut at 70mph, or similar.
Promoters denounce sceptics as saying that helmets are "worthless" and ridicule the idea that they provide no benefit |
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| mainly sceptics | Cycling has been around for 125 years, after all. |
| Begging the Question | promoters, sceptics to a lesser extent | How could anyone be opposed to a law which would result in more people wearing a life-saving device? (begs the question of whether helmets save lives)
Helmets should be compulsory because promotion alone is not enough (begs the question of whether helmet use is worth increasing in the first place)
Note: <a href="logical-fallacies#begging">begging the question</a> means including the conclusion in the premises of the question, not inviting or demanding the question. |
| Burden of Proof | promoters | Promoters routinely challenge sceptics to disprove the idea that helmets prevent serious injuries, save lives or whatever. This is a clear reversal of the burden of proof, which should (and does) lie with those proposing an intervention. It is fair for the sceptic to say: "Prove it." It is not scientifically acceptable for the promoter to say: prove me wrong, or I am right. |
| Complex Question | probably both | You should be in favour of cycle helmets and protecting children
You should be opposed to helmet promotion and pavement cycle lanes. |
| Fallacies
A fallacy is, at its most basic, simply a false statement. Here are some of the more common variants: |
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| promoters | Literature reviews and meta-analyses of helmet efficacy very frequently fall into this trap by failing to include, whether by accident or design, sources which might contain conflicting evidence. A particularly extreme and unsubtle example of the fallacy of exclusion was provided by the troll known as <a href="mini-faq-johndoh">John D'oh</a>
This fallacy is mainly the preserve of promoters because the pro-helmet evidence is so widely promoted as to make ignoring it futile; I do not claim that we are especially virtuous in this regard. |
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| promoters | "50 children under the age of still die [annually] of cycling head injuries" - Angela Lee. The real figure is ten and falling. |
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| possibly both | There is an apparent dichotomy in the BMA's current stance, in that they support cycling as a healthy activity but nonetheless advocate use of protective equipment, but this is a weak example as the BMA stance is based on false evidence. |
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| promoters | Any "helmet saved my life" anecdote |
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| unknown | Arguably this applies to the 1989 Seattle study, in that it confuses two definitions of "cyclists wearing helmets", but that's stretching a point. |
Non-Sequitur: affirming the consequent
| promoters | If helmets save lives then helmet use should be compulsory. But helmets are not proven to save lives. |
Non-Sequitur: denying the antecedent
| sceptics | If helmets reduce injury then it would be obvious in New Zealand; it is not so they don't. Actually this partially equivocation, in that they may well prevent injuries falling below the threshold of recording. So in this statement (which is true enough if injury is replaced with serious or fatal injury) the reduction in trivial injuries is denied on spurious grounds. Not a very good example, but there you are. |
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| promoters | Something must be done, this is something, therefore this must be done. |
| Fallacies of Definition |
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| promoters, maybe both | Helmets reduce serious brain injuries because they spread the impact across the skull. The statement does not prove that this is the mechanism underlying brain injury, or indeed that helmets do so to any meaningful extent. |
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| promoters, maybe both | Helmets should be compulsory because everybody should wear one. |
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| promoters | Anybody who has hit their head while wearing a helmet and not been injured, will be glad they were wearing a helmet. The subject group can't really come to any other conclusion. |
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| sceptics, perhaps? | I thought that claims along the lines of "helmets grab the tarmac and make rotational injuries worse" would fit, but there is evidence for grabbing and evidence for rotational injuries, just no documented link between the two, making it more of a non-sequitur. Better example needed. |
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| promoters | Helmets prevent injuries, so should be promoted. The definition of injuries is too broad: form a public policy perspective, trivial injuries are generally unimportant. |
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| sceptics, probably promoters | Helmets do not prevent serious or fatal injuries, so should not be worn. The definition excludes types of injuries which may be painful or inconvenient, if rare. |
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| both | The entire hypothesis of helmet use cannot be scientifically tested because randomised controlled trials would be unethical
The theory of risk compensation is inherently untestable as one cannot prove a negative. |
| False Generalisations
False generalisations arise when an individual case is assumed to be representative or indicative of the general case. These are like inductive fallacies but fall short of the appearance of statistical validity. |
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| promoters | Any shroud-waving, helmet saved my life or other anecdote. |
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| promoters, maybe sceptics | You say that helmeted riders are less cautious; I know I am no less cautious when helmeted, therefore I reject the idea of risk compensation. |
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| unknown | Is Coulthard's "wear a helmet, I don't" plea under this heading? |
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| promoters | Shroud-waving again. Also pro-helmet studies. |
| Gambler's Fallacy | unknown | <img width="1" height="1" src="/icons/ecblank.gif" border="0" alt=""> |
| Genetic Fallacy | sceptics | Any research from CDC, Puget Sound is automatically suspect because it comes from the Thompsons and Rivara. But all evidence must be judged on its merits. |
| Guilt by Association | sceptics, some promoters | Any reference to the 1989 Seattle study, any claim from BHIT (well, it's possible they might do their homework sometimes, isn't it?); to discredit these by reference to earlier, flawed work is to be guilty of this fallacy. |
| Hubris | promoters, mainly | "Steven M. Scharf is one of Earth's leading experts on bicycle helmets" - <a href="Scharf">Steven M Scharf</a>. Er, quite. |
| Inductive Fallacies
These are fallacies in what is purportedly inductive reasoning (A is true, A implies B, therefore B is true). In each case either A is not true, or A does not imply B, therefore B is not necessarily true - the existence of a fallacy does not prove that B is false, it simply does not prove that it is true. |
Biased or Unrepresentative Sample
| promoters | A core fallacy in <a href="http://www.cyclehelmets.org/mf.html#1038" target="_blank">the 1989 Seattle study</a>, and many other <a href="observational_studies">observational studies</a>. |
Causation vs. Correlation ''' or '''Common Cause
| both, mainly promoters | Again, a core fallacy in observational studies; also sceptics discussing injury rates in different countries. |
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| promoters | Any reference to motorcycle helmets or construction workers' hard hats. |
False Categorisation: Composition
| promoters | See <a href="observational_studies">observational studies</a>. |
False Dilemma or False Dichotomy
| proponents | Would you rather hit your head while wearing a helmet, or while not wearing one? The fallacy being in the assumption that the likelihood of hitting your head is independent of whether you are wearing a helmet; it almost certainly is not, although to what degree it is dependent is open to speculation.
The correct answer to this question is of course: "no,thanks." |
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| both, mainly sceptics | Helmet use is not proven to reduce serious injury, therefore it does not
Helmet use is not known to increase rotational injury, therefore it does not. |
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| promoters | Any "<a href="http://www.cyclehelmets.org/mf.html#1019" target="_blank">helmet saved my life</a>" anecdote. |
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| promoters | Cyclists suffer head injuries in collision with cars; therefore helmets should be worn. First, helmets are not designed for these collisions, second, the collisions should be averted rather than a subset of injuries possibly mitigated. |
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| promoters, maybe sceptics | Helmets work thus, therefore they prevent injury. How the helmet works is of no relevance.
Helmets grab tarmac, therefore they increase rotational trauma. This is essentially untested. |
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| promoters | Observational studies. |
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| promoters | Angela Lee on the deterrent effect of helmet laws on levels of cycling: "That doesn't happen. It depends how you promote it. Anyway, it's all in here (pointing to her left temple), if it's promoted positively there will be no decrease." |
| Middle Ground | promoters | Extreme A: Helmets should be mandatory for all
Extreme B: Helmets should not be worn
False midpoint: Helmets should be compulsory for children.
The fact that the "midpoint" lies between two apparent extremes of an argument has no bearing on whether it is right or not. |
| Red Herring | both | Changing the topic under discussion does not address the merit of a claim - everyone does that sometimes :-) |
| Straw Man | both | You dispute that helmets save lives, so you are anti-helmet and that is ridiculous because...
You promote helmets, so you think they can prevent impacts from fast-moving juggernauts and that is ridiculous because... |
