The effect of eradicating poverty on childhood unintentional injury mortality in New Zealand: a cohort study with counterfactual modelling

Background: The aim of this study was to examine the effect of household income on unintentional injury mortality in children and to model the potential impact of eradicating income poverty as an injury prevention strategy. Methods: A national retrospective cohort study linking census to mortality records carried out in New Zealand during a 3-year period following the 1991 census and including children aged 0-14 years on census night. The main outcome measures are odds ratios (ORs) for unintentional injury death by equivalised household income category and proportional reductions (population-attributable risk) in unintentional injury mortality from modelled scenarios of nil poverty. Results: One-third of children lived in households earning less than 60% of the national median household income. Age-adjusted odds of death from unintentional injury were higher for children from any income category compared with the highest, and were most elevated for children from households earning less than 40% of the national median income ( OR 2.81, 95% CI 1.73 to 4.55). Adjusting for ethnicity, household education, family status and labour force status halved the effect size ( OR 1.83, 1.02 to 3.28). Thirty per cent of injury mortality was attributable to low or middle household income using the highest income category as reference. Altering the income distribution to eradicate poverty, defined by a threshold of 50% or 60% of the national median income, reduced injury mortality in this model by a magnitude of 3.3% to 6.6%. Conclusions: Household income is related to a child's risk of death from unintentional injury independent of measured confounders. Most deaths attributable to low income occur among households that are not defined as "in poverty''. The elimination of poverty may reduce childhood unintentional injury mortality by 3.3% to 6.6%.