In Retail trade and Trade and repair of motor vehicles and motorcycles, volume indices are obtained by deflating the value indices by a price index which is representative of the products sold and obtained by aggregating the household consumer price indices of the products concerned. It is therefore considered that for a given activity the price index of the sector changes in the same way as the sector price index. We establish a cross-reference table between the sectors of the Naf rev 2 and the nomenclature of consumer function, constructed by disaggregation of the European nomenclature - COlCP - for CPIs and retail trade. For each industry, CPIs are aggregated from the previous year's CPI structure to calculate the overall price index.

It is not enough to deflate the turnover indices in value excluding VAT by the consumer price indices to determine volume indices. Indeed, CPIs are measured with all taxes included. To eliminate the impact of price changes from CPIs, it is therefore necessary to correct the impact of changes in VAT rates.

Wholesale trade covers all goods produced (new or used). For sales volume indices in wholesale trade, we thus use according to the products: IPGA (Wholesale food Price Index), IPAMPA (Monthly Agricultural means of production purchasing price index), IPPAP (Monthly Agricultural Producer Price Index), IPPI (French Industry Production Price Index for the French Market - Market Price or Base Price) and Consumer Price Indexes.

The product weights of each sub-sector used to construct the aggregate price index (the sum of the weights is equal to 1) are derived from the sector x product matrix established by the INSEE's "Commerce Division" . This breakdown into products is made at the very fine CPF 6 level (French product classification), according to the sales structure of the annual sector survey (ESA).

The sectoral index is therefore a weighted average of the various indices representing the products making up the sales structure according to the ESA survey in 2010.

The volume indices of sales at a fine level are defined as the ratio of the turnover index in value to the associated price index. This is done for the 116 subclasses of the trade sector.

Once the indices at the finest level of nomenclature are calculated, the indexes of the sectors with the highest nomenclature levels can be calculated by aggregation.

The indices of the broader sectors are computed by Laspeyres indexes (with constant weights over time) from the most detailed indices. They are rebased every 5 years; The indices currently published use  base 2010, ie the weightings of the different levels correspond to values ??calculated for the year 2010. They are also published in reference 100 in 2010 i.e. the indices have a mean of 100 in 2010.

The constant weightings of the elementary indices relate to production sold in the branches in 2010 at basic prices. By definition, production at basic prices excludes taxes on the products, but includes subsidies on products; transport services are not included. Weightings are calculated using data from national accounts and the annual sector survey 2010.

The series are corrected for seasonal adjustments (SA) and calendar effects (working day adjustments WDA). An estimate of these effects is produced with the X12-Arima software in JDemetra+ (supplied by Eurostat) at the classes level of NAF rev. 2. This correction is made at the level of the "volume" ratio, ie raw index of turnover in value / raw price index. SA-WDA indices for higher levels are obtained by aggregating the SA-WDA indices of the classes that make up the level.

The annual mean of the SA-WDA indices can slightly differ from that of the raw indices because it takes into account variations from one year to the next in the annual composition in working days: presence of leap years, position in the week of various public holidays, and so on.