Replicating Japan's CPI Using Scanner Data

We examine how precisely one can reproduce the CPI constructed based on price surveys using scanner data. Specifically, we closely follow the procedure adopted by the Statistics Bureau of Japan when we sample outlets, products, and prices from our scanner data and aggregate them to construct a scanner data-based price index. We show that the following holds the key to precise replication of the CPI. First, the scanner databased index crucially depends on how often one replaces the products sampled. The scanner data index shows a substantial deviation from the actual CPI when one chooses a value for the parameter associated with product replacement such that replacement occurs frequently, but the deviation becomes much smaller if one picks a parameter value such that product replacement occurs only infrequently. Second, even when products are replaced only infrequently, the scanner data index differs significantly from the actual CPI in terms of volatility. The standard deviation of the scanner data-based monthly inflation rate is 1.54 percent, which is more than three times as large as that for actual CPI inflation. We decompose the difference in volatility between the two indexes into various factors, showing that it mainly stems from the difference in price rigidity for individual products. We propose a filtering technique to make individual prices in the scanner data stickier, thereby making scanner data-based inflation less volatile.