On paper, Wanganui households spent $7,798 on food in 2014. The year before? $15,641. A 50% drop in twelve months.

If that sounds impossible, it's because it is.

This isn't a story about Wanganuians suddenly eating half as much. It's about a measurement change that shows how careful we need to be when data suddenly shifts. Between 2013 and 2014, something fundamental changed in how Stats NZ tracked food spending in this region. The methodology shifted, the sample changed, or the geographic boundaries were redrawn.

What makes this particularly striking: Wanganui's food spending had been remarkably stable for years. (Source: Stats NZ, food-price-index-detailed) In 2010, it was $14,652. By 2013, it had crept up to $15,641. A gradual, predictable climb that reflected normal inflation and population changes.

Then 2014 hits, and the number cuts in half.

This matters because food price data is everywhere right now. Politicians cite it. News outlets report it. Families use it to understand why their grocery bills feel crushing. But when the underlying measurement changes, comparing year to year becomes meaningless.

The 2014 figure of $7,798 is the lowest Wanganui food spending has been since 1993. But you can't celebrate that as progress, because it's not measuring the same thing the earlier years were measuring.

Here's what this data actually teaches us: be suspicious of dramatic one-year changes. When a number that's been stable for years suddenly halves, the story isn't in the number itself. It's in what changed about how we're counting.

For Wanganuians trying to understand their real cost of living in 2014, this figure tells them almost nothing. It's a statistical artefact, not a reflection of what was actually happening in their kitchens and supermarkets.

The broader lesson applies to all regional economic data. When Stats NZ updates methodology, redefines regions, or changes sample sizes, it creates these discontinuities. The numbers are technically accurate, but comparing them across the break is like comparing apples to oranges.

And critically: these are nominal figures, not adjusted for inflation. Even if the 2014 number were directly comparable to 2010, you'd need to account for four years of inflation to understand what changed in real terms.

The real story here isn't about Wanganui. It's about reading data carefully. When something looks too dramatic to be true, it usually is.