Why would it shock you? Think about it for a minute. Collecting CPI data is simple, although a big logistical exercise: go to the shops and write down current p

Why would it shock you? Think about it for a minute. Collecting CPI data is simple, although a big logistical exercise: go to the shops and write down current prices (for 1000 shops and 1000 goods). Collecting aggregate sales data has to be done at a different point - more easily done by surveying companies or collecting export/import volume data. This is done too - but only quarterly and only published way after the end of the quarter, rather than prices that are collected monthly and published after 2 weeks. It is also done by a different agency, the BEA calculate Personal Consumption Expenditure (the volumes consumed) while the BLS collects CPI (price inflation data).