Age distributions

“Bowel cancer does not discriminate on race. Māori and Pacific peoples have a similar risk of developing bowel cancer compared to other population groups at a given age.

“It was true that a higher proportion of bowel cancers occur in Māori and Pacific peoples at a younger age, but that is because the overall demographics of those groups are younger. It has always been age that determines bowel cancer risk, not race”

I thought that this required more explanation. Proportion at an age does not seem to me to depend on the demographics of those ages

It’s a good question.  The minister is plausibly correct that the younger age at diagnosis for Māori and Pacific Peoples is driven substantially by demographics.   That is, one reason that few very elderly Māori get diagnosed with bowel cancer is that there aren’t many very elderly Māori.  Fewer Māori make it to be very elderly, and also the Māori population is increasing both because of higher birth rate and because more people are now identifying as Māori to the healthcare system.   If you have the same age-specific incidence rates in two groups, but one group averages younger, the incidence in the younger group will tend to be at younger ages.

That’s not the whole story, or even most of it, for this decision.  The age distribution being quoted is age at diagnosis (because that’s what you have for cancer), but diagnosis isn’t equally distributed. According to the HQSC atlas of health care variation, Māori are more likely to be diagnosed with bowel cancer following emergency presentation, and more likely to die within two years of diagnosis. This means there’s a good case that Māori are more underdiagnosed than New Zealand Europeans.   On the other hand, a lot of the problem with underdiagnosis is not being tested. If people end up just doing one test when they become eligible, and then not bothering later, the optimal age for a single test is more like 60 than 50.   And, as a general principle,  if you want to spend public money to improve health, you typically will do better by spending it on people who are less healthy and have worse access to health care.

In any case, while the headline Bowel cancer screening eligibility age to be lowered for everyone is technically true (since the lower-age screening pilot has already been stopped), it seems to miss the point a little.