Editing Consumer price index (section)

===Estimating weights===
The outlet and regional dimensions noted above mean that the estimation of weights involves a lot more than just the breakdown of expenditure by types of goods and services, and the number of separately weighted indices composing the overall index depends upon two factors:
# The degree of detail to which available data permit breakdown of total consumption expenditure in the weight reference-period by type of expenditure, region and outlet type.
# Whether there is reason to believe that price movements vary between these most detailed categories.

How the weights are calculated, and in how much detail, depends upon the availability of information and upon the scope of the index. In the UK the retail price index (RPI)<ref>{{Cite web|url=https://www.investopedia.com/terms/r/rpi.asp|title = Retail Price Index (RPI) Definition}}</ref> does not relate to the whole of consumption, for the reference population is all private households with the exception of pensioner households that derive at least three-quarters of their total income from state pensions and benefits, and "high income households" whose total household income lies within the top four per cent of all households. The result is that it is difficult to use data sources relating to total consumption by all population groups.

For products whose price movements can differ between regions and between different types of outlet:
* The ideal, rarely realizable in practice, would consist of estimates of expenditure for each detailed consumption category, for each type of outlet, for each region.
* At the opposite extreme, with no regional data on expenditure totals but only on population (e.g. 24% in the Northern region) and only national estimates for the shares of different outlet types for broad categories of consumption (e.g. 70% of food sold in supermarkets) the weight for sliced bread sold in supermarkets in the Northern region has to be estimated as the share of sliced bread in total consumption × 0.24 × 0.7.

The situation in most countries comes somewhere between these two extremes. The point is to make the best use of whatever data are available.

Due to differences in weightings in the consumer basket, different price indices may be calculated for groups with various demographic characteristics. For example, consumer price indices calculated according to the weightings in the consumer basket of income groups may show significantly different trends.<ref>{{Cite journal |last=Daşdemir |first=Esat |date=2022-04-15 |title=A New Proposal for Consumer Price Index (CPI) Calculation and Income Distribution Measurement by Income Groups |url=https://iupress.istanbul.edu.tr/en/journal/jecs/article/gelir-gruplarina-gore-tuketici-fiyat-endeksi-tufe-hesaplari-ve-gelir-dagilimi-olcumu-icin-yeni-bir-oneri |journal=Journal of Economy Culture and Society |language=en |volume=0 |issue=65 |pages=395-414 |doi=10.26650/JECS2021-984480 |issn=2602-2656}}</ref>