Molcho and Pickett criteria

Molcho and Pickett1 propose that the following are deemed unacceptable: ‘(1) intentional injuries; (2) severe, fatal, or disabling injuries; (3) injuries occurring while involved in unhealthy, unnecessary, or abnormally risky behaviours; and (4) injuries that occurred while ignoring known preventive measures. However, injuries that are unintentional, occurring during a necessary or health generating activity, and that do not have long-term implications could be viewed as acceptable, after weighing the benefits of engagement in healthy activities with the risks for injury and trauma.’

Operationalising some criteria is problematical

The authors do not address the operational aspects of their proposal, and herein lies the major challenge to what they propose. For example, what measures and thresholds would we use to decide whether the activity was necessary and did not have long-term consequences? How often would we have the information to weigh the benefits of engagement in healthy activities with the risks of injury? Rivara2 in his counterpoint raised similar concerns when he asked whose norms should we use when deciding whether or not an activity that gives rise to injury is ‘regular/normative’.

The authors also suggest that an injury only has to meet one of the non-acceptable criteria to be deemed ‘non-acceptable’. This is problematical. For example, climbing over a farm barbed wire fence is typically unnecessary, as there is normally a gate relatively close by, and it is risk generating, as there is a risk of laceration. So why do people do this? We suggest it is often the case that they cannot be bothered going out of their way to use the gate given that they judge the risk of injury to be low and, in the event of being injured, the injury is likely to be minor in terms of threat to life or threat of disability. It is for the latter reasons that prevention and policy makers should be uninterested in such minor/superficial injury events.

A focus on important injury is enough

We have previously argued that the focus of injury prevention should be on important injury (irrespective of age), defined as those injuries, irrespective of intent, which represent a high threat to life, high threat of disability, or high cost.3 This emphasis aligns reasonably well with Molcho and Pickett's severity criterion. We believe this severity criterion is sufficient to focus our prevention efforts. We note that Rivara's counterpoint to the Molcho and Pickett1 commentary also focused on this aspect of the proposal.2

Defining serious injury

A critical issue that has not been sufficiently articulated in either paper is that around defining what is serious non-fatal injury? Molcho and Pickett1 refer to ‘severe’ and ‘disabling’ injury. What would constitute ‘severe’ or ‘disabling injury’?

Many authors, and the general public, consider any injury that requires inpatient treatment is by definition serious, and by implication those that do not require such treatment are less serious. Rarely is the underlying construct of seriousness clearly defined.

Historically, the most commonly used concept of severity is that associated with anatomical or physiological damage to the body that in turn has been related to threat to life. A widely accepted measure of anatomical damage is the abbreviated injury scale (AIS).4 AIS is an anatomically based, consensus derived, global severity scoring system that classifies an individual injury (classified by nature and by body site) according to its relative severity on a six-point scale. Table 1 shows the distribution of AIS scores for patients who were discharged from a public hospital in New Zealand in 2010. International Classification of Disease version 10-AM codes were converted to AIS98 codes using the software developed by the European Center for Injury Prevention at the University of Navarra.5

According to AIS, only 14% of the 43 894 hospitalised injuries were serious (AIS 3) or worse.

Anatomical damage or physiological damage to the body should not be the sole means of determining thresholds for acceptable injury because many injuries that are ‘minor’ in this respect are ‘serious’ in terms of disability. For example, an injury to an eye will never score a high AIS score but nevertheless could have devastating consequences, such as blindness.

Most minor threat-to-life injuries are not disabling

Using quality-adjusted life-years lost, McClure and Douglas6 have shown that the lifetime estimates of morbidity resulting from injuries not considered serious enough to admit to hospital were of an order of magnitude higher than those that resulted in either death or hospitalisation. They went on to argue that their study provides a strong argument for the recognition of the public health importance of minor injury (ie, non-hospitalised injury). What McClure and Douglas6 failed to do was to determine if a subset of the non-hospitalised injuries were accounting for the major portion of the costs. We use New Zealand injury cost data to show how important such a disaggregation of quality-adjusted life-years losts might be.

The Accident Compensation Corporation (ACC) manages New Zealand's ‘no-fault’ comprehensive injury cover for all New Zealand residents and visitors.7 Injured people can apply for assistance, no matter how they became injured, or whose fault it was. The assistance can include a wide range of services from payment for treatment and equipment, to help with income if the injured people can no longer work. Because of the wide range of help available from ACC after an injury, people cannot sue for personal injury in New Zealand, except for exemplary damages. Approximately 7% of the new injury claims registered with ACC each year potentially require compensation and/or support for returning to independence (eg, income support, home support or assistance with returning to work). These are referred to as entitlement claims.8 Those injured people who seek treatment in the acute phase of their treatment (typically from a general practitioner) and do not make any subsequent claim for services are referred to as medical fees only claimants.

Table 2 shows that while medical fees only claims represent the vast majority of all claims, the average cost is relatively low and cumulatively they only represent 11% of the total injury costs. At most approximately 58 000 (4%)9 would have been from people who were treated in hospital for their injury.

We need to develop threat of disability tools

There is an operational constraint on our proposal that the focus of injury prevention should be on important injury. While we have the tools available to determine, from population-based injury data, those injuries that should be a priority in terms of threat to life,5 10 no equivalent threat of disability tools have been developed and successfully applied to population-based injury databases. We believe research investment in this area would be far more useful than seeking to operationalise the other criteria Molcho and Pickett1 propose.

Final remarks

We have previously argued that studies need to make explicit their theoretical and case definitions of injury.11 It will be clear from the foregoing that this recommendation is equally important for conversations about severity. It is important that authors when describing the severity of injury are explicit about the underlying construct they are referring to. Is it threat to life, threat of disability, cost, or some other construct? This also has ramifications for the titles of papers. For example, we suggest that Rivara's counterpoint, which is entitled ‘Minor injuries may not be all that minor’, would have been more appropriately titled ‘Some injuries which represent a low threat to life may represent a significant threat of disability’.

In summary:

1. We agree that it is reasonable to focus our preventive efforts on a subset of injuries.

2. Some of Molcho and Pickett's criteria are unworkable.

3. It is enough to focus on injury, which is important in terms of threat to life, (threat of) disability, cost, or some other explicitly stated dimension of severity/burden.

4. Threat of disability tools that can be applied to population injury data are in urgent need of development.

5. It is important that authors, when describing the severity of injury, are explicit about the underlying construct they are referring to.