October 8, 2013

Death rate bounce coming?

A good story in Stuff today about mortality rates.

A Ministry of Health report shows while death rates are as low as they have even been since mortality data was collected, men are far more likely to die of preventable causes than women.

Heart Foundation medical director Professor Norman Sharpe said it is a gap that will continue to widen as a “new wave” of health problems caused by obesity start showing up in the statistics.

The latest mortality data, gathered from death certificates and post-mortem examinations, shows there were 28,641 deaths registered in New Zealand in 2010.

While the number of actual deaths is increasing, up 8 per cent since 1990, this was because of a growing and ageing population.

Death rates overall have dipped about 35 per cent, meaning statistically we are more likely to survive to a ripe old age.

There aren’t any of the problems I complained about in last year’s story on this topic: there’s a clear distinction between increases in rates and the impact of population size and aging, and the story admits that the problems with preventable deaths it raises are projections for the future.

While on this topic, I will point out a useful technical distinction between rates and risks.  Risks are probabilities; they don’t have any units and are at most 100%. Lifetime risks of death are exactly 100%, and are neither increasing nor decreasing.  Rates are probabilities for an interval of time; they do have units (eg % per year). Rates of death can increase or decrease, as the one death per customer is spread out over shorter or longer periods of time.


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »


  • avatar

    The underlying item makes clear that the discussion of differences between male and female mortality rates from preventable causes was in relative terms. The item thus reflects the common misperception that increases in mortality will tend to increase relative differences between mortality rates of groups with higher and lower rates. Exactly the opposite is the case. Increases in mortality tend to reduce relative differences in mortality while increasing relative differences in survival.

    See generally my:

    (1) Can we actually measure health disparities? Chance 2006:19(2):47-51: http://www.jpscanlan.com/images/Can_We_Actually_Measure_Health_Disparities.pdf

    (2) Race and mortality. Society 2000;37(2):19-35: http://www.jpscanlan.com/images/Race_and_Mortality.pdf

    See with respect to New Zealand my:

    (1) The importance of distinguishing mortality inequalities from survival inequalities. Journal Review Feb. 17, 2010 (responding to Hill S, Sarfati D, Blakely t, et al. Survival disparities in indigenous and non-indigenous New Zealanders with colon cancer: the role of patient comorbidity, treatment, and health service factors. J Epidemiol Community Health 2010;64:117-123): http://jpscanlan.com/images/Hill_JECH_2010.pdf

    (2) Interpreting changes in mortality differences. J Epidemiol Community Health Sep. 8, 2005 (responding to Shaw C., Blakely T., Atkinson J., Crampton P. Do social and economic reforms change socioeconomic inequalities in child mortality? A case study: New Zealand, 1981-1999. J Epidemiol Community Health 2005;59:638-644): http://jech.bmj.com/content/59/8/638.abstract/reply#jech_el_347

    For illustrations of the way that, as the population ages and mortality rates generally increase, gender difference in mortality rates decrease while gender differences in survival rates increase, see the Life Table Information document associated with the Life Table Illustrations subpage of the Scanlan’s Rule page of jpscanlan.com: http://jpscanlan.com/images/LIFE_TABLE_INFORMATION.pdf

    4 years ago

    • avatar
      Thomas Lumley

      That isn’t the point here. They aren’t saying this is a general principle about death rates, they are saying that men in New Zealand have a specific set of risk factors, less common in women, that they expect to lead to higher rates of preventable death in the future.

      4 years ago