NZ Government's trend analysis of hospitalised self-harm is misleading

The aim of this paper is to demonstrate that the trends published in the New Zealand (NZ) Government's 2006 Suicide Trends document for hospitalised self-harm are misleading.

Analysis of incident self-harm events resulting in hospitalisation and reference to published material on injury outcome indicators for the NZ Injury Prevention Strategy (NZIPS).

The significant increase in rates of self-harm hospitalisation presented in Suicide Trends from 1989 to a large extent reflect changes in recording practice rather than any change in self-harm in the community. Indicators with significantly fewer threats to validity suggest there has been little, if any, increase in the incidence of self-harm. The authors of Suicide Trends did not adequately specify how they defined a case and, moreover, their methods were not consistent with those used for the NZIPS indicators.

The methodological challenges to producing valid indicators for the purposes of measuring trends in important non-fatal injury are substantial. Unless we accept that the usual methods of measuring trends in non-fatal injury are misleading and commit to taking up the challenge to produce and use better indicators, we will continue to run the risk of misleading ourselves and the public.