 The Commission also found that 99% of all data were collected during the week, although an increasing amount of purchases happen during the weekend.Additional bias was said to stem from changes in retailing that were unaccounted for in the CPI.Some critics believe however, that because of changes to the way that the CPI is calculated, and because energy and food price changes were excluded from the Federal Reserve's calculation of "core inflation", that inflation is being dramatically underestimated.