In 2010, Timaru's food price index sat at 14,599. By 2013, it had climbed steadily to 15,445. Then something strange happened: in 2014, it halved to 7,836.

This wasn't a price crash. Nobody in Timaru suddenly started paying half as much for bread and milk. What happened was a change in how Statistics New Zealand measures food prices, a rebasing of the index that reset the reference point. The numbers tell you nothing about what happened in Timaru's supermarkets. They tell you everything about the fragility of how we track the cost of living.

Here's why this matters: food price indices are designed to show trends over time. You're supposed to be able to compare 2010 to 2014 to 2020 and see whether your grocery bill is getting more expensive. But when the index gets rebased, that continuity breaks. The 7,836 figure from 2014 can't be compared to the 15,445 from 2013. They're measured on different scales.

For Timaru residents watching their budgets, this is more than a statistical quirk. It means the data that's supposed to help them understand whether their grocery bills are genuinely rising or falling has a blind spot. Between 2010 and 2013, the index rose by 846 points, a steady climb that matched what people felt at the checkout. Then the data goes dark for a year.

Stats NZ rebase indices periodically to reflect changes in what people actually buy. We eat less beef than we used to, more avocados. We buy different brands. The basket needs updating. But the cost is a gap in the historical record, a moment where the data stops being useful for the very thing it's meant to do: track change over time.

This isn't unique to Timaru. Every region goes through this. But Timaru's 2014 drop is one of the starkest examples of how rebasing can make a dataset look broken. If you were trying to write a story about food prices in South Canterbury over the past decade, you'd hit 2014 and the numbers would stop making sense.

The broader point: we rely on these indices to tell us whether we're better or worse off. They inform policy, wage negotiations, household budgets. But they're not as solid as they look. They're constructed, periodically rebuilt, and sometimes they leave gaps. The 7,836 figure isn't wrong. It's just not comparable to what came before. And that matters when you're trying to understand whether your grocery bill has doubled in a decade or stayed flat. (Source: Stats NZ, food-price-index-detailed)