Something strange happened to Wanganui's food prices between 2013 and 2014. The index didn't fall. It didn't crash. It halved.

For four years running, the figure had been climbing steadily: 14,652 in 2010, 15,404 in 2011, holding at 15,641 for both 2012 and 2013. Then 2014 arrived, and suddenly the number was 7,798. The lowest reading in 21 years.

This wasn't a sale at Pak'nSave. This was Stats NZ changing how it counts.

What likely happened: a methodological shift, a reclassification, or a change in how regional data gets weighted and reported. Maybe Wanganui got absorbed into a broader regional grouping. Maybe the basket of goods being measured changed. Maybe the sample size shrank.

The problem isn't that these changes happen. It's that they make decades of data impossible to compare. You can't track the real cost of feeding a family in Wanganui over twenty years when the measuring stick gets cut in half halfway through.

This matters because food price data is how we understand whether life is getting more expensive. It's how policy gets made. It's how wage negotiations happen. It's how journalists write stories about the cost-of-living crisis.

And when the numbers jump or drop by 50% overnight for purely administrative reasons, it becomes impossible to tell the difference between a genuine price shock and a spreadsheet reshuffle.

Wanganui isn't unique here. Regional food price data across New Zealand is patchy, inconsistent, and frequently revised. Some regions get granular tracking. Others get lumped together. Some years have detailed breakdowns. Others don't.

The 2014 discontinuity in Wanganui's data is a reminder that the numbers we use to measure our lives are fragile. They're built on definitions, classifications, and methodologies that can change without warning. And when they do, we lose the ability to see clearly what's actually happening to the price of bread, milk, and meat.

If you're trying to understand whether your grocery bill has doubled in the last decade, you need data that doesn't suddenly change its mind about what it's measuring. Wanganui's vanishing index is a case study in why that's harder than it should be.

(Source: Stats NZ, food-price-index-detailed)