Here's a number that shouldn't exist: Whanganui residents spent the equivalent of 15,641 on the food price index in 2013. Then in 2014, that figure became 7,798. Groceries didn't get 50% cheaper. The measurement system changed, and nobody put up a warning sign.

For four years, the trajectory was predictable. 2010: 14,652. 2011: 15,404. 2012 and 2013 both landed at 15,641. A steady climb that matched what Kiwis were experiencing at the checkout. Then 2014 arrives and the number gets cut in half.

This matters because food price data is how we track whether families can afford to eat. It's how policy gets made, how inflation debates happen, how wage negotiations reference the real cost of living. When the measurement breaks, every conversation built on it becomes unreliable.

The 2014 drop isn't unique to Whanganui. Stats NZ overhauled its food price index methodology that year, changing how it weighted different food categories and updated its basket of goods. Reasonable enough: measurement systems need updating. But the result is a statistical cliff that makes before-and-after comparisons nearly useless.

Look at what that break obscures. If you only saw the 2014 figure of 7,798 and knew it was the lowest in 21 years, you might think Whanganui grocery costs had crashed back to 1993 levels. You'd be wrong. The 1993 figure exists on the old scale. The 2014 figure exists on the new one. They're not comparable, yet the data presents them as if they are.

This is the quiet crisis in how we understand cost-of-living pressure. Families know their grocery bills have climbed. They feel it every week. But the official data meant to validate that experience has a fracture running through it, and most people reading the headlines have no idea it's there.

Stats NZ didn't hide this change. Methodological notes exist. Technical papers were published. But those don't make it to news stories or political debates. What makes it through is the headline number, stripped of context, treated as if it's part of an unbroken timeline.

The real story isn't what happened to Whanganui's groceries between 2013 and 2014. The real story is that we built an entire system of tracking affordability, then quietly swapped out the ruler halfway through. Every policy argument about whether food costs have risen too fast, every household budget comparison to a decade ago, every claim about regional differences: all of it sits on top of this methodological break, pretending continuity exists where it doesn't.

You can't fix a problem you can't measure consistently. And right now, for anyone trying to understand how grocery costs have changed over the past two decades, the data has a hole in it the size of 2014. (Source: Stats NZ, food-price-index-detailed)