How Fast Are Prices in Japan Falling?

物価は経済の「体温」と言われるが、その喩えを使えば消費者物価統計は「体温計」である。体温計を変えると数値はどれくらい変わるのだろうか。こうした問題意識から、本論文では「体温計」を取り換えて日本の体温を測り直すという実験を行った。具体的には、サンプル抽出方法として、（1）我が国の消費者物価統計を作成している総務省の方法に近いもの、（2）総務省の方法に似てはいるが特売価格の扱い方などいくつかの点で異なる方法、（3）米国の消費者物価統計の作成機関である労働統計局が採用している方法、の3種類を試した。実験の結果、総務省方式に近い方法でサンプル抽出した場合には、消費者物価の公表数字に近い数字が得られた。また、総務省の特売価格の扱いを変更するなどしてもさほど変わらなかった。しかし、米国型のサンプル抽出を採用した場合は、結果に大きな違いが見られた。

The consumer price inflation rate in Japan has been below zero since the mid-1990s. However, despite the presence of a substantial output gap, the rate of deflation has been much smaller than that observed in the United States during the Great Depression. Given this, doubts have been raised regarding the accuracy of Japan's official inflation estimates. Against this backdrop, the purpose of this paper is to investigate to what extent estimates of the inflation rate depend on the methodology adopted. Our specific focus is on how inflation estimates depend on the method of outlets, products, and price sampling employed. For the analysis, we use daily scanner data on prices and quantities for all products sold at about 200 supermarkets over the last 10 years. We regard this dataset as the "universe" and send out (virtual) price collectors to conduct sampling following more than 60 different sampling rules. We find that the officially released outcome can be reproduced when employing a sampling rule similar to the one adopted by the Statistics Bureau of Japan. However, we obtain numbers quite different from the official ones when we employ different rules. The largest rate of deflation we find using a particular rule is about one percent per year, which is twice as large as the official number, suggesting the presence of substantial upward bias in the official inflation rate. Nonetheless, our results show that the rate of deflation over the last decade is still small relative to that in the United States during the Great Depression, indicating that Japan's deflation is moderate.