International comparisons of injury mortality in the elderly: issues and differences between New Zealand and the United States.

BACKGROUND

International comparisons of mortality rates for injury, as for other conditions, can suggest priorities for further research and intervention. However, variability in the assignment of underlying cause, especially among the elderly, may lead to difficulty in interpreting cross-national differences in death rates. Despite similarities between the two countries, the injury death rate for ages < or = 65 in New Zealand is substantially higher than the United States rate. The objective of this study was to investigate possible reasons for this difference.

METHODS

We used data not previously reported for New Zealand to calculate the cause-specific injury death rates for ages > or = 65, compared them with US rates, and examined other injury rates that could help explain the observed difference.

RESULTS

The New Zealand death rate from falls for ages > or = 65 was nearly three times the US rate (92 versus 32 per 100,000), causing the death rate for all injuries in this age group to be 34% higher in New Zealand (153 versus 114 per 100,000). However, hospitalization rates for both falls and hip fractures are similar for the two countries.

CONCLUSIONS

The substantially higher fall injury death rates for older New Zealanders are not fully explained by differences in the incidence of falls resulting in injury nor the case fatality rate for fall-related injury. US injury death rates based on underlying cause of death might be similar to New Zealand rates, and thus substantially higher, if subjected to comparable procedures for the completion and coding of death certificates. As in studies of other conditions, international comparisons of injury death rates based on underlying cause, especially in studies of the elderly, must consider variation between countries in death certification and coding practices.