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Main points of the 2015-base revision

  We began to release the 2015-base CPI in August 2016. The 2010-base CPI will also be calculated and published until December 2016. The following points of the 2015-base CPI is revised.

(1) Revision of the CPI base period

  The index reference period and weight reference period of the CPI are revised from 2010 to 2015. We release the 2015-base index from January 2015 retroactively, and the indices before December 2014 are converted into the 2015-base and linked to enable time-series analysis. However, the rates of change are not recalculated with the linked index but the published values for every base period are used unmodified.

(2) Weight revision

  The weights used for the 2015-base CPI are calculated on the basis of average household expenditures by item per month in 2015, principally derived from the Family Income and Expenditure Survey (concerned with two-or-more-person households).

(3) Revision of items

  Items whose importance for household consumption expenditure has increased or decreased are added or removed respectively from the index items. As a result, the number of items used for the 2015-base index is 585 (Added items: 33 items; Removed items: 32 items; Integrated items: 8 into 4 items).

(4) Revision of the price index calculation method using a model formula

  Some items such as airplane fares, electricity and mobile telephone charges have various fare structures, with prices that vary according to the purchased conditions. To accurately reflect the price fluctuation in the price index, monthly indices for these items are calculated with a special formula (model formula) which is designed by using a typical utilization case of each item as a model. We revise the component ratios of prices and the choices of model cases used in model formulae to accurately reflect actual conditions to the price indices.

(5) Revision of publishing series and classification items

  In 2015-base CPI, we release new index series described below.
  Given the aging of population, an index based on the expenditure composition for subgroup index for retired elderly households the head of which is over 65 years old is included. In order to enhance the convenience of index, the series including fresh food calculated by Laspeyres' chain index method are released not annually but monthly in 2015-base CPI. In addition, CPI rounded to three decimal places is available for users' convenience in replicating the published rate of change.

  For further information, please refer to "2015-Base Explanation of the Consumer Price Index".

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