A tale of two mortality decades

This post updates data for New Zealand.  It shows how much the rate of improvement in mortality has slowed in the years 2010-2018 compared to 2000-2010.

Previous posts showed that mortality improvement in New Zealand had not slowed as dramatically as seen in other countries and that a slowdown in life expectancy gains was a bigger problem in Great Britain than in New Zealand or Australia.

Reasons why this might be happening, and why it matters, are here.

New Zealand’s mortality rates, or death rates, for ages 50 and over from 1971 to 2018 are shown below.  The picture is of a long-term falling trend, but the trend slows in later years.Reminder: a fall in death rates means mortality is improving, adding to longer lifespans. A slowdown or stalling in the trend line may be a cause for concern.

International research has focused on 2010-2012 as the period when the trend to slower rates began.  For this New Zealand analysis, trend lines have been drawn on the age-specific death rates for 2000-2010, and for 2010-2018.

A slowdown would mean the later trend line has a lower rate of change than the earlier.  These two charts show this to be the case across all age groups over age 50, except for females aged 90 and over.For both males and females under age 64, the rate of improvement has been noticeably reduced in the later period, to the extent of becoming a small worsening of mortality rates in the second period for males aged 50-54 and females aged 55-59.

The patterns are similar for males and females which indicates that the driving factors for the slowdown apply across the population. The shape across ages suggests a cohort effect – perhaps that an important contributor to the slowdown is that improvements in causes of death which most affect the younger end of this age range have run out of steam (as death rates in those age groups are now very low).

The slowdown in mortality rates will be reflected in estimates of future life expectancy.  But, despite the slowdown in mortality improvement, there have been more years of mortality improving than the reverse.  The long-run trend is still that the life expectancy of the New Zealand population continues to increase.  Average lifespans are getting longer, just not as fast as they once were.



All calculations on data from Stats NZ Age-specific death rates by sex, December years (total population) Downloaded 12 April 2019.  Trend lines are calculated as the basis for finding rates of change as raw data has year-by-year volatility, but the shapes of the annual rates of change based on raw data are similar.


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