Many more prisoners identifying as Ngapuhi

Corrections Volume Report 2019-20 has just been released. I had a quick scan through for anything particularly noticeable. These two graphs caught my eye:

(The Ngapuhi number is 609 - off the graph.)

The immediate inference is that iwi-affiliated offending and imprisonment is going through the roof. But consider this graph:

This is a conundrum. The iwi-identifying number is increasing whereas the Maori number is decreasing.

4,907 prisoners are Maori. 2,498 state one of the iwi affiliations above. About half.

My conclusion is that prisoners are increasingly identifying with an iwi. I wonder why? Bet there is some sort of incentive. Sudden radical changes in data are usually driven by a specific, but not necessarily obvious reason.

Is the Ngapuhi Treaty settlement actually going to happen??

But the plot thickens. In 2018, from the Minister:

Mr Davis said Māori make up over 50 percent of the prison population, and he wants that number reduced.

"Of that 50 percent, half again, are from Ngāpuhi, my own tribe, so this is personal.

"My tribe of Ngāpuhi is probably the most incarcerated tribe in the world, per head of population, so we really have to look at what we're going to do differently as a country, to turn these figures around."

Yet the just-released stats show there were 668 Ngapuhi prisoners in 2018.

Perhaps Mr Davis is encouraging the trend in order to validate his claim?