Declines in the Lethality of Suicide Attempts Explain the Decline in Suicide Deaths in Australia

BACKGROUND: To investigate the epidemiology of a steep decrease in the incidence of suicide deaths in Australia. METHODS: National data on suicide deaths and deliberate self-harm for the period 1994-2007 were obtained from the Australian Institute of Health and Welfare. We calculated attempt and death rates for five major methods and the lethality of these methods. Negative binomial regression was used to estimate the size and significance of method-specific time-trends in attempts and lethality. RESULTS: Hanging, motor vehicle exhaust and firearms were the most lethal methods, and together accounted for 72% of all deaths. The lethality of motor vehicle exhaust attempts decreased sharply (RR = 0.94 per year, 95% CI 0.93-0.95) while the motor vehicle exhaust attempt rate changed little; this combination of motor vehicle exhaust trends explained nearly half of the overall decline in suicide deaths. Hanging lethality also decreased sharply (RR = 0.96 per year, 95% CI 0.956-0.965) but large increases in hanging attempts negated the effect on death rates. Firearm lethality changed little while attempts decreased. CONCLUSION: Declines in the lethality of suicide attempts-especially attempts by motor vehicle exhaust and hanging-explain the remarkable decline in deaths by suicide in Australia since 1997