yeah, i don't love my discretionary/essential breakdown there. it's more about the combo of essential + non-exchangeability -- you need a car but there are a lot of options, but when you need a hospital there's usually one best place. (and education is non-exchangeable due to competitiveness).

the other big correlate is just goods vs services (even textbooks are service-like due to editions). I am not an economist but I'm really curious whether rapid depreciation caused by planned obsolescence of e.g. consumer electronics is causing a poor measurement of price trends in that area. Today's iPhone will cost much less next year, but the cost of maintaining a cutting-edge smart phone keeps going up.