Picture a Timaru household in late 2013, watching their grocery bills climb year after year. The food price index for their region had risen steadily from 14,599 in 2010 to 15,445 by 2013. Then, overnight in the data, it halved.

By 2014, that same index read 7,836. Not a gradual decline. Not a correction. A collapse so abrupt it takes you back to 1993 to find anything comparable.

This isn't a story about cheaper groceries. Nobody in Timaru suddenly started paying half what they paid the year before. This is a story about broken data, and what happens when the numbers we rely on to understand cost-of-living pressures simply stop making sense.

For three consecutive years before 2014, Timaru's food price index climbed incrementally: 14,599, then 15,309, then 15,343, then 15,445. The trajectory was clear. Families were spending more. Then the index lost half its value in a single reporting period.

Two possibilities exist. Either Stats NZ changed how it measures food prices in Timaru mid-stream (a methodology shift that wasn't flagged in the data), or something went wrong in the collection process. Either way, the result is the same: a four-year trend line that tells you nothing useful about what actually happened to food costs in one South Island city.

This matters because food price data isn't academic. It informs policy. It shapes how we talk about cost-of-living crises. It tells families whether their rising grocery bills are a personal problem or a national one. When the index drops by 7,609 points in twelve months, it doesn't reflect reality. It reflects a system failure.

Timaru isn't unique in having patchy regional data, but this drop is extreme enough to raise questions about how many other regional datasets contain silent breaks like this. If you're a researcher trying to track food inflation in smaller centres, or a councillor trying to understand why families are struggling, you're working with a ruler that changed length halfway through the measurement.

The 2014 figure now sits as the lowest in 21 years. Not because Timaru got cheaper. Because something in the data collection chain snapped, and nobody bothered to explain why the numbers suddenly told a completely different story. (Source: Stats NZ, food-price-index-detailed)