and work time) and the costs of medical treatment. If some of these costs are not borne by the individual, and are therefore not reflected in his willingness to pay, the value of the avoided costs must be added to WTP to measure the social benefits of reduced injuries.

Estimates of individual WTP to avoid injury can be measured using revealed or stated preference approaches; however, empirical estimates of WTP to avoid risk of injury exist for very few categories of injury. This is in part due to the wide variety of injuries to be valued (see Table 5). The more common approach is to produce an estimate of the medical costs and lost productivity associated with an injury—the so-called direct and indirect Costs of Illness. Cost of Illness (COI) estimates may either be used as a lower bound to WTP or may be supplemented with estimates of the quality-adjusted life years (QALYs) lost due to the injury. QALYs measure the extent to which an injury (or illness) limits physical or social functioning or causes discomfort. QALYs are often monetized, using the VSLY, and monetized QALYs added to COI estimates to produce a more comprehensive estimate of the value of avoided injury.

This section discusses both components of injury costs—estimates of the Cost of Illness and monetized QALYs. We review COI estimates of injury costs in the US and discuss sources of data for estimating these costs in developing countries. This is followed by a brief discussion of QALY indices and their application to measuring healthy life years lost to injury. The practice of monetizing QALYs is controversial; however, failure to monetize QALYs often results in using only COI estimates, which are a lower bound to the value of avoided injury. The issue of monetizing QALYs is discussed in Section D. Because of the effort involved in computing bottom-up estimates of injury costs for a variety of injuries, it may be useful first to compute back-of-the envelope estimates of injury costs. Approaches to computing rough estimates of injury costs are suggested in section E., based on the results of US studies.

# B. Cost of Illness Estimates

Estimates of the medical costs associated with an injury depend on the level of treatment received as well as on the unit costs of medical personnel, emergency room visits and hospital stays. In the United States large-scale health surveys are used to estimate the costs of hospitalized and non-hospitalized injuries, by ICD-9 code (Corso et al., 2006). These surveys describe both the level of treatment received for an injury, a doctor diagnosis of the injury and the costs of treatment.<sup>35</sup> Corso et al. (2006) use these data to estimate the costs of all injuries in the United States for 2005, by ICD-9 and AIS threatto-life code. Robinson (2007) summarizes the present value of lifetime medical costs of injuries reported in Corso et al. (2006) by AIS code. Medical costs per person increase from $1,000 for minor injuries (AIS 1) to $67,000 for critical injuries (AIS 5).

There is, however, significant variation in medical costs by body region, holding AIS code constant. Table 9, from Zaloshnja et al. (2004) shows medical cost estimates for road traffic crash survivors, broken down by AIS code and body region. Spinal cord

> 35 The Medical Expenditure Panel Survey (MEPS) is once source of information and the Healthcare Cost and Utilization Project another.

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