National Statistics, Republic of China (Taiwan)

The prices of the goods and services purchased for consumption purpose by households nationwide (excluding Kinmen County and Lienchiang County).

For fresh vegetables, fruits and fish products and related, factual prices are collected on the days in the month whose last digit happen to be 2, 5, or 8. The rest of the items are collected on the days in the month whose last digit happen to be 5.

To measure the average changes of prices in consumption products (including goods and services) generally purchased by households nationwide (excluding Kinmen County and Lienchiang County).

I. Index base period：2021 = 100

II. Rate of change：%

1. I. Basic Group：Contains a general index and the indices for 7 groups, 40 subgroups, and 62 small groups as well as indices for 368 items.
2. II. Special Group： 

1. 1. Indices classified by commodity and services type, which contain the indices for 2 groups and further into 14 subgroups.
2. 2. Indices classified by purchase frequency：to buy about once a month, to buy about once every three months and to buy about once longer than three months.
3. 3. Indices for households in different disposable income groups：lowest 20% disposable income group, middle 60% disposable income group, and highest 20% disposable income group.
4. 4. Elderly Household：Index based on households that are comprised solely with persons aged 65 years and over.

Five working days.

1. 1. From the base year of 1996, the DGBAS introduced the relative importance to compile the indices, the link period is next Dec. of base year, and the previous indices were untouched.
2. 2. From 2009, elementary aggregates are calculated by geometric averages.
3. 3. From Feb. 2011, the DGBAS began publishing the indices classified by 3 income group：Low (Lowest 20% households with Disposable Income), Mid (60% of households with Disposable Income) and High (households with Disposable Income).
4. 4. From the base year of 2011, new index categories, by Frequency of Purchase and Elementary Aggregations, were added.
5. 5. From the base year of 2016, the weights of the groups and priced items are revised annually in order to go in line with the current expenditure structure of households, and using the December of the Reference year for linking period. However, reviewing the classification of the groups and the priced items are done once every 5 years.
6. 6. The price items weights of year t CPI should have adopted the household consumption structure in year t–2 except 2023 and 2024. As the control restrictions of COVID-19 were eased since the third quarter of 2022, consumption in 2023 has gradually returned to normality, which is very different from the 2021 epidemic period. 2023 price items weights of CPI adopt the structure of the three-year average consumption over 2019 to 2021, rather than 2021. 2024 CPI weights adopt the consumption structure from the fourth quarter of 2022 to the third quarter of 2023.
7. 7. From the base year of 2021, CPI for Elderly Household will be published annually. From Jan. 2025, CPI for Elderly Household will be released on a monthly basis ,with retrospective release of monthly data since 2018.

I. Compilation:

1. 1. Formula：The general index and group indices (except vegetables and fruits) are computed by the derived from of Laspeyres Weighted Aggregate Formula, and the weight of all items (except vegetables and fruits) and groups are updated annually. The weight of fresh vegetables and fruits adopt monthly varying weights according to the monthly sales of recent 3 years moving average.
2. 2. Yearly index：The yearly index is the arithmetical average of the monthly indices, rounded to nearest hundredth.
3. 3. Treatment for lack of priced items：If the item of a specific brand is out of supply on market, a similar commodity bearing a different brand is priced and the adjustment should be made according to the following formula：Price of substitute commodity at base period = (Price of originally surveyed commodity at base period) / (Price of originally surveyed commodity at period prior to current one) × Price of substitute commodity at period prior to current one

II. Data Source：

1. 1. Price Localities：9 cities (i.e. New Taipei, Taipei, Taichung, Tainan, Kaohsiung, Taoyuan, Hsinchu, Keelung and Chiayi) and 8 counties (i.e. Yilan, Miaoli, Nantou, Yunlin, Pingtung, Taitung, Hualien, and Penghu). Another 3 counties (i.e. Hsinchu, Changhua and Chiayi) only survey Residential Rents .
2. 2. Date of Pricing：The date of pricing is determined by the feature of the priced items. Some Items with high price fluctuation (e.g. fresh vegetables and fruits) may be priced 3 times a month, the other items may be priced once a month.
3. 3. Survey Agency：The Office (Department) of Budget, Accounting and Statistics of the surveyed city or county is designated as the survey agency.

The yearly index is the arithmetical average of the monthly indices, rounded to nearest hundredth. The group indices are weighted average from the price relatives of the priced items.