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Q&A about the Consumer Price Index

[A. About the consumer price index (CPI)]

A-1 What is CPI all about?

A-2 Since when has the CPI been calculated?

A-3 What is the the index reference period? And what is the weight reference period?

A-4 How is the CPI used?

A-5 What indices do they use for measuring underlying inflation?

[B. Calculation of the CPI]

B-1 How do you calculate the CPI?

B-2 Is the CPI calculation method of Japan as same as that of major countries?

B-3 How do you select items used in calculation of the CPI?

B-4 How do you calculate the CPI for clothes and other commodities whose distribution and sales differ considerably from one season to another?

You seem to survey the prices of summer and winter clothes when they come on the market seasonally. Yet how do you calculate the CPIs for those months not directly covered by the survey?

B-5 What is imputed rent of an owner-occupied house?

[C.Uses of the results]

C-1 When are results published?

C-2 Do you publish a seasonally-adjusted CPI?

[D. Revisions to the bases]

D-1 Why is the CPI revised?

D-2 Isn't the CPI's base revision interval of five years too long to cope with rapid changes in the consumption pattern?

D-3 At the base revision of the CPI, how do you link old indices and new indices?

D-4 What kind of impacts does the base revision have upon year-on-year percentage changes and contributions to the total change of the CPI?

D-5 How much impact did the 2025-base revision have on year-on-year percentage changes?

D-6 What are the differenecs in year-on-year percentage changes between the 2025-base revision and the previous base revisions?

[E. Midpoint-year review]

E-1 What is a midpoint-year review?

[F. Quality adjustment]

F-1 What is quality adjustment with CPI for, and how do you make it?

F-2 What is the hedonic method?

F-3 I heard that, with the hedonic method, the price of an item is considered to be gone half off if its performance has doubled. Is this true?

[G. Frequently asked questions about the CPI]

G-1 One new product after another shows up on the market. Does the CPI survey reflect prices changes of these new products?

G-2 Are private brand commodities surveyed?

G-3 Are discount stores included as survey subjects?

G-4 Will the CPI appropriately reflect the change of quality such as functional improvement of products?

G-5 It is said that there is an upward bias in Japan's CPI. Is this true?

G-6 I heard that Japan has adopted a different method for selecting products subject to the RPS from that of the United States.

Is Japan's selection method different from other countries?

G-7 Is there anything I should note when I compare the CPI and Corporate Goods Price Index (CGPI) published by Bank of Japan?

G-8 I hear that the CPI and the GDP deflator (Published by the Cabinet Office) are different from each other. Why is this?

G-9 Recently, there have been instances in some media reports where price indices based on POS data are compared with the Consumer Price Index(CPI). What points should one keep in mind when reviewing such comparisons?

G-10 Sometimes new products are released that have the same price but offer a smaller quantity or are lighter in weight. Are these so-called "hidden price increases" reflected in the Consumer Price Index?

G-11 What is the fixed specifications method?

[H. Consumer Price Index calculated by Laspeyres' chain index method]

H-1 What kind of index is "Consumer Price Index calculated by Laspeyres' chain index method" compiled as one of the supplementary indices?

H-2 How is the chain index calculated?

H-3 What is the difference in the rate of change between the chain index and the fixed base Laspeyres index?

H-4 Why do you position the chain index as a supplementary index?

[I. Consumer Tax]

I-1 Does the CPI include the Consumer Tax?

[Others]

1 If price data cannot be collected due to the impact of the COVID-19 pandemic, such as temporary store closures or temporary product shortages, how is the Consumer Price Index calculated?

2 Due to the COVID-19 pandemic, overseas package tours were suspended and resumed after 2020.Have you taken any measures regarding "Charges for package tours to overseas" index?

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