The classification system also considers consistency with producer price index's commodity classification and with time series continuity of price indices. Prices for owner-occupied housing units are imputed using the equivalent rent method. In the future, it is planned to update expenditure weights every two years.
Sample sizes are centrally determined, based on generics' relative price variability and weight.
Samples for each city in the index are revised at approximately two year-intervals. Prices collected each day are sent electronically to the Bank of Mexico. An individual ten digit code is also assigned to each specific product. Discontinued items are substituted by new products which are as similar as possible. An investigation is carried out with outlet officials to assure that the substitute market share is similar to that of the original item.