Prices Analytical Series
Technical Supplement for the March 2021 Consumer Price Index

Beginning in April 2020, the collection and compilation of the Consumer Price Index (CPI) have been impacted by measures designed to limit the spread of COVID-19, as in-person field collection was conducted remotely, and imputation strategies were required to address an increased number of temporary business closures and out-of-stock products. These strategies were implemented according to international guidelines, and following consultation with other national statistical organizations.

Where outlets remained temporarily closed, items were out of stock at a higher rate than usual or products and services remained unavailable for consumption, the imputation treatments for the March CPI were the same as those used since the onset of the pandemic.^Note 

Tables reflecting product and outlet availability (Table 1), imputation donors for unavailable products and services (Table 2) and CPI sub-components with an out-of-stock rate above 30% (Table 3) have been updated to reflect March data.

Adjustments for imputed classes following the resumption of their availability to consumers

Products that are not available for consumption in a region for one or more months are imputed as described in Table 2. When a product becomes available for consumption again, an adjustment factor is calculated to ensure the index reflects only observed price movements. The price relative in the month when availability resumes will be the ratio between the current observed price over the last observed price adjusted for the impact of imputations. As a result, the impact of the imputed price movements is limited only to the months when the product was not available for consumption.

For example, for a given product / geography, if,

• in March 2020, it was available for consumption and prices were observable
• in April 2020, it was unavailable for consumption and prices were not observable
• in May 2020, it was unavailable for consumption and prices were not observable
• in June 2020, it was available for consumption again and prices were observable,

then

• in April 2020, the price index between March 2020 and April 2020, $I^{{}^{202003:202004}}$ , was imputed.
• in May 2020, the price index between April 2020 and May 2020, $I^{{}^{202004:202005}}$ , was imputed.
• in June 2020,
• the price index between March 2020 and June 2020, $I^{{}^{202003:202006}}$ , is calculated using prices observed in March 2020 and June 2020,
• the price index based on observed prices is adjusted by the sequence of imputations, so that the final price index between May 2020 and June 2020 is calculated as $I^{{}^{202005:202006}}=I^{{}^{202003:202006}}/(I^{{}^{202003:202004}}*I^{{}^{202004:202005}})$.

This treatment corresponds to the approach used for the re-introduction of seasonal products in the CPI in the first month of their in-season period.^Note   For products/services that have not been available for consumption for many consecutive months, and are seasonal in nature, alternative treatments may be required.

Additional questions about how the CPI accounts for outlets remaining temporarily closed, items out of stock at a higher rate than usual, or products and services remaining unavailable for consumption due to COVID-19 can be directed to statcan.cpddisseminationunit-dpcunitedediffusion.statcan@canada.ca.