The weights of the Consumer Price Index (CPI) and the Harmonised Consumer Price Index (HICP) are updated each year. They are used to aggregate the 21,000 indices calculated by family of elementary products and geographic area of collection. These weights represent the share of expenditure associated with the index concerned with regard to household consumption covered by the CPI/HICP.

The HICP brings together approximately 30,000 elementary indices. An elementary index generally represents the cross-referencing of one consumption segment and one urban unit ('var-agglo').

First-level or elementary-level indices are calculated using non-weighted aggregation formulas because there is insufficient data to weight the elementary observations within each pairing (consumption segments x urban units). Two formulas are used according to the type of consumption segment:

• if the consumption segment consists of highly comparable products in terms of their quality, the Dutot formula will be applied;

• if the consumption segment consists of excessively heterogeneous products, the Jevons formula will be applied.

Monthly

Price collections performed in the field (except for centralised collection) are carried out by different operators whose roles are described in detail below.

The collectors collect the prices of the goods and services that constitute the CPI in the different retail outlets via a tablet computer over a four-week period. They propose replacements for missing products and replacements for retail outlets when they are permanently closed.

INSEE collectors must examine the labels or tariffs that shops are legally required to display. They move around freely without being accompanied of the store department manager.

Collectors transfer their collections to the IT centre on a daily basis.

Managers of Price Sites are responsible for ensuring compliance with all procedures designed to guarantee the integrity of the statistical methods adopted. Managers organise the price collectors' collection rounds, track and monitor how the collection is progressing, and evaluate the collected data (including data checking). They participate in the launch of search orders and their monitoring during year change operations (OCA) for the implementation of the new sample in January of the following year (N+1). They also participate in the training of collectors (continuing and possibly initial).

The Bordeaux Price Centre is dedicated to the online collection of prices of durable goods (see sheet 1.1). This centre centralises requests for the replacement of durable goods. When durable goods are replaced, the collector is asked to submit two proposals: the Price Site checks the existence of the proposed references and the Bordeaux centre verifies the technical characteristics before choosing the most appropriate product to replace the one that has disappeared (in certain cases, by using a hedonic model).

Dedicated and secure applications are used to carry out all of these verifications and data checking operations.

The CPI Division at Head Office is responsible for design, methodology and quality control. It retrieves the calculated indices (via the IT applications after data checking), checks consistency and analyses the observed changes. The Price Division collects prices from certain price lists, calculates the index of centralised consumption segments and the overall index.

Every year, it updates the sample in order to reflect actual consumption more closely. It sends guidelines to the Price Sites on the creation, removal or modification of consumption segments. These guidelines state the number of different products desired and the distribution per form of retail outlet, in addition to the removal or addition of the urban units required to carry out the new collection. Each year, 10 to 20% of the products in the list of consumption segments are reviewed in this way.

The Price Division publishes the provisional results of the index for month m on around the 30^th^ day of each month m and the definitive results on the 13th of the following month in a publication called Information Rapide, accompanied by a brief comment.

An IT team from the national IT centre in Paris manages the applications.

Data are validated at different level of the statistical process: collection of the data, sample design, methodology.

The HICP is an annually chained Laspeyres-type index which allows the weights to be changed on an annual basis.

The indices at the consumption segment level are calculated by the weighted sum of the elementary indices divided by the elementary indices for month 0 (December of the previous year); the weights correspond to the sampling weights of the urban units.

The prices are recorded as displayed in the retail outlets, generally to 2 decimal places and the weights are applied to 40 decimal places. The values are not truncated at the different calculation stages. However, the published indices are rounded up to 2 decimal places and the variations calculated on the basis of the published indices are rounded up to 1 decimal place.

No adjustment is made.