• Interventions
• public health
• methods
• MVTC
• methodology
• surveillance
• populations/contexts
• child

The arguments put forward by Langley and Cryer1 are interesting, thoughtful, but entirely wrong. This means that some of the views put forward by Molcho and Pickett2 are also wrong. Langley and Cryer assert that ‘it is unrealistic and counterproductive to try and prevent all childhood injury.’ They add that this ‘prevent all’ so-called ‘paradigm’ should extend to all age groups. I agree with the all age point but reiterate that the proponents of this paradigm (of whom I am one) are indeed seriously suggesting that we must seek to prevent even the ‘mildest’ of injuries. We do so simply because it is impossible to accurately predict the outcome of most injury events.

Langley and Cryer give the example of ‘a child tripping over and sustaining a barely visible abrasion to the arm.’ Ordinarily this should be little cause for concern and we need not move heaven and earth to try to stop this specific trip. But consider this: a child tripping causes the injury. This means that some part of the body strikes some surface. Now let us suppose that the body part is the head and the surface is concrete. Or that the tripping occurred on an elevated surface such that the distance fallen is greater. The result is likely to be much more serious than a scratched arm; it could just as well be a concussion, or worse.

I was asked to provide evidence to support my argument. I cannot find suitable data but perhaps this mental experiment would help. Take the most common injury—a fall—and start with the usual outcome, a scrape or bruise. Now add just a bit of momentum to the victim; imagine that person running and then tripping, and think about the outcome. Maybe just a bad bruise but maybe if the runner lands on an outstretched hand the result is a Colles' fracture, especially if the person is elderly. Or imagine that instead of falling on a carpeted floor the surface happens to be littered with broken glass and the result is a severed blood vessel. The outcome depends on extremely small variations in the components: the speed, the height, the surface, etc. ‘If I had struck it a few inches (centimetres) to the left, the result would have been disastrous!’

My point is that unless Langley and Cryer can assure us that whenever someone trips they can guarantee only a scratched arm will result, we need to try to prevent all such injury sequences because we cannot predict the consequence. It is easy if we talk about ‘acceptable’ and ‘unacceptable’ in terms of severity because logically everyone would agree: we can tolerate the trivial and struggle to prevent the severe. But how do we know which result will follow any specific event? Langley and Cryer challenge Molcho and Pickett to address operational aspects of their proposal. In turn, I ask if any of these authors can provide data that show that defining seriousness by outcomes (whether based on hospitalisations, anatomic or physiological damage) can be regarded as anything more than a variant on ‘post hoc ergo propter hoc’ reasoning, which, I remind you, is fallacious.

In case you are not yet convinced, examine the two sides with a particular preventive measure in mind: bicycle helmets. Because most bicycle mishaps do not result in a severe injury, Langley and Cryer would logically have to propose that only those likely to experience such an injury wear helmets. I hope most readers would agree it makes much more sense for everyone to do so. Or consider the example of speeding: most speed-related crashes cause more damage to cars than drivers and so are they suggesting that only those likely to result in severe body injuries need to slow down? If so, how do we identify those drivers and how do we then ‘target’ our preventive efforts at them and only them?

Langley and Cryer also argued that it is unrealistic to try to prevent all injuries. But is it really? Is not what they are proposing the less realistic alternative? They are, in effect, suggesting a high risk, targeted approach to prevention. What I am proposing is a population strategy. Which is more realistic? I see an analogy with the late Geoffrey Rose's position3 regarding salt and hypertension: he viewed it as more realistic and more effective to try to reduce salt intake in the entire population than to do so only for those who were hypertensive or likely to become so. Similarly, I ask if it makes sense to try to only target those who are likely to trip, fall and then be concussed, or to propose measures that will prevent most from tripping. Whether those measures involve shoes with Velcro straps instead of laces, or sidewalks without holes or bumps, these seem far more feasible than some mysterious approach aimed at those destined to have the falls resulting in a severe injury—an approach that Langley and Cryer judge to be ‘sufficient’ as a focus for prevention efforts.

In essence, their whole argument is based on the astonishing and presumptuous assumption that the outcome of an injury event can be accurately predicted in all instances. It is only if this is possible that the criterion ‘do not have long-term implications’ can be met. I contend that short of passing a soothsayer course with flying colours, this is not possible. What might have helped illuminate this discussion is some indication from Langley and Cryer if they were referring to primary, secondary or tertiary prevention. Doing so would help relate their thinking to that of Haddon4 who conceptualised the sequence as preevent, event and postevent. He proposed that there were prevention opportunities at each stage but when he focused on the preevent he did not adjust his views based on whether the injury was destined to be minor or severe. (Probably the reason he did not was that even Haddon could not predict the future!) I assume that it is primary or secondary that is the focus of the prevention Langley and Cryer have in mind and I acknowledge that the secondary question is more complex and contentious than the primary. Nevertheless, let me give an example to better explain what I mean.

A bicyclist is riding slowly down the street when suddenly a car door opens and he strikes it. He is wearing a helmet so a secondary prevention measure is in place. But does this event qualify for something worth preventing according to Langley and Cryer? Given the slow speed, the usual result would be little more than a few bruises. But, if the collision resulted in the bicyclist going over the door and landing head and face first on the road, the result could be a fractured nasal bone and several lacerations. The helmet prevented a concussion for which the victim (me) is certainly grateful. On another occasion, I fractured a clavicle when I fell (was pushed) down a few stairs. Foresight would suggest there might be no need to worry about two or three stairs; hindsight tells a different, more painful story. My point should be clear: the circumstances of an injury do not permit accurate predictions of the consequences and we cannot base policy on reasoning backwards!

Finally, Langley and Cryer also state that the paradigm they are criticising is ‘counterproductive’. Much of what I have written addresses whether it is realistic, but I fail to understand why that view should be seen as counterproductive. Perhaps they could elaborate on the reasoning behind this puzzling assertion.