How do different definitions of ‘serious injury’ overlap? A case study based on TAC compensated traffic injuries in Victoria (2006-2010)

Background: The outcomes of road traffic injury can be viewed through a number of lenses, including: threat to life, impairment, pain and suffering, quality of life loss, cost and resource use. While numerous definitions of ‘Serious Injury’ exist based on these aspects, there is no consensus on the most appropriate definition.
Aim: To understand how different definitions of ‘Serious Injury’ correlate and overlap.

Method: Serious injury was defined in four ways, these being threat to life,
impairment, compensation cost, and resource use as indicated by a length of stay of at least 15 days in hospital. The sample consisted of 67,797 road users injured in Victoria in the period 2006 – 2010 inclusive, and who made a claim for compensation to the Transport Accident Commission (TAC). Analysis was performed to investigate the relationship between four definitions of serious injury and an Euler diagram was developed to study the overlap between them.

Results: There were significant, but moderate, correlations between all pairs of serious injury measures. In addition, the Euler diagram analysis showed that the cohorts of claimant classified as serious injury by the four different definitions showed only partial overlap, with only 0.6% of claimants classified as ‘serious’ by all four definitions with a far higher proportion classified as serious by one definition of serious injury. Conclusions: The importance of identifying a common, comprehensive definition of serious injury that is robust cannot be underestimated. The analysis presented here suggests a composite measure of serious injury is required.