A Timaru household watching their grocery receipts in late 2013 would have seen an index reading of 15,445. Twelve months later, that same household, buying roughly the same basket of goods, would have seen a reading of 7,836.

That's not deflation. That's not a price war at Countdown. That's a statistical reset, and it tells us something important about how we measure the cost of living in regional New Zealand.

For context: between 2010 and 2013, Timaru's food price index climbed steadily from 14,599 to 15,445. A gradual increase, the kind you'd expect over four years of normal inflation. Then the index halved overnight in 2014, dropping to 7,836. (Source: Stats NZ, food-price-index-detailed)

This wasn't unique to Timaru. Stats NZ rebased its entire food price index in 2014, changing the reference year and recalibrating how the numbers are calculated. What looks like a collapse in grocery costs is actually a methodological shift: the agency updated what goes into the basket, how items are weighted, and which year serves as the baseline.

But here's why it matters beyond the technicalities. When you're comparing food prices across decades, these breaks in the data create blind spots. A politician might say groceries cost half what they did in 2013. Technically true if you only look at the index numbers. Completely misleading if you're trying to understand what actually happened to household budgets.

The 2014 rebase means you can't draw a straight line from the early 2010s to today without accounting for the discontinuity. Any analysis that treats 7,836 as genuinely lower than 15,445 is comparing apples to a completely different variety of apples, measured on a different scale.

For Timaru families, the actual experience was this: groceries got more expensive between 2010 and 2013, just like everywhere else in New Zealand. Then in 2014, the way Stats NZ counted those costs changed. The prices in the supermarket didn't halve. The index did.

This is the kind of thing that makes cost-of-living debates so slippery. The numbers are real. The methodology is sound. But unless you know where the statistical furniture got rearranged, you can end up telling a story that never happened.

Timaru's 2014 figure isn't the lowest in 21 years because groceries got cheaper. It's the lowest because that's when the measuring stick changed. The lesson: always check what's behind the number before you decide what it means.