It's clearly not "completely" disconnected, otherwise there would be zero volatility in supermarket prices. But again a price is a price not matter what layer of the market it sits at, and all prices are subject to market conditions. Freaking out about some subsampling of them as being "real" in/de/stag/whateverflation in an attempt to shoehorn whatever noisy data you have into a signal that confirms your priors just leads to the kind of nonsense logic that produced the analysis I quoted above.
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It's clearly not "completely" disconnected, otherwise there would be zero volatility in supermarket prices. But again a price is a price not matter what layer of the market it sits at, and all prices are subject to market conditions. Freaking out about some subsampling of them as being "real" in/de/stag/whateverflation in an attempt to shoehorn whatever noisy data you have into a signal that confirms your priors just leads to the kind of nonsense logic that produced the analysis I quoted above.
I understood that supermarkets are always changing prices semirandomly, so that consumers never really know what the price "should" be.