Objectives: The aim of the present study was to clarify the extent to which the recorded marked decline in young male suicide (20-34 years) in Australia since 1998 is attributable to misclassification of cause of death information.
Methods: Secular trends in young male suicide rates were investigated for the period 1976-2005. Suicide rates in the period after the peak of the epidemic in this age group (1998) were re-calculated based on published estimates of under-enumeration of suicide data, and misclassification of likely suicide cases to other unintentional and undetermined external causes. Two misclassification scenarios were used to revise young male suicide rates from 1998: previously reported estimates of 9% under-enumeration due to misclassification of unintentional causes of death, and 17% under-enumeration due to misclassification of open cases in addition to unintentional causes of death. All-cause mortality was also examined.
Results: Recorded male suicide in the 20-34 year age group increased over the study period, peaking in 1998 at 39 per 100,000, before declining sharply in the period 1999-2005 by 44% to 22 per 100,000 in 2005. Following adjustment for misallocation under the first scenario, suicide rates declined 38% to 24 per 100,000, and under the second scenario declined 33% to 26 per 100,000. Revised suicide rates were not materially different from recorded suicide rates based on 95% confidence intervals over this period. All-cause mortality declined from 1999 due to reductions in suicide and other causes.
Conclusion: The recent marked decline in young male suicide in Australia is real. The effects of misallocation of likely suicide cases to other causes did not substantially affect population trends in suicide rates in the period after 1998. There is still a need to account in detail for why young male suicide has declined so substantially during the period after 1998.