January 23, 2014

Really the worst?

Stuff has a story saying NZ is the worst in the world for bowel cancer, according to new World Health Organisation statistics. We’ve looked recently at claims that NZ was 2nd worst and 3rd worst in the world on various measures. They weren’t true. This one isn’t true either, though as with the previous stories, the truth is that NZ is still pretty bad.

The Herald story is more accurate, saying that Australia and New Zealand are the highest; that’s still a bit misleading because it just means the highest among regions, not countries, and because the region is dominated by the Australian data.

Since the stories are calling for more screening, it doesn’t really make sense to look at rates of diagnosis (‘incidence’). Incidence rates can only go up with increased screening, not down — the whole point of screening is to increase diagnosis. It makes more sense to looks at rates of death from bowel cancer (though the claims aren’t actually true for incidence, either).

If we use the new World Health Organisation statistics that both stories mention, and compare deaths from bowel cancer (as a fraction of the whole population, standardised for age) to all the countries for which the World Health Organisation has data, we find that NZ is second-worst in women (the gray line) and the rate of death is almost twice that for Australia.

female-mortality

In men, New Zealand is 25th-worst, and about 50% higher than Australia

male-mortality

Going for the ‘worst in the world’ title has led to missing a real public-health fact from the new statistics: NZ fatal bowel cancer rates compare much less favorably in women than in men, whether the comparison is to the whole world or to Australia.

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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 »

Comments

  • avatar
    Margaret Arnold

    I understand that the incidence of bowel cancer is related to the latitude of the country — and at New Zealand’s latitudes rates are all high other than for Japan, which is one reason why vitamin D is thought to have a important role in the bowel cancer rates.

    This might mean of course having a screening/education programme is even more important here.

    7 months ago Reply

  • avatar
    Megan Pledger

    The interesting thing is the difference in male and female rates (not that much) and the difference in rank (quite a lot). Usually diet is the big risk factor e.g. meat which men tend to eat more of even after taking into account their size; whereas this suggests something environmental which both genders are exposed to.

    7 months ago Reply

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