The survey “Observation of Prices in Industry and Services” attempts to measure gross price developments (not seasonally adjusted). The price response series received from the "suppliers" are converted into basic series in the form of reference indexes (base year) and are then aggregated into index series according to an aggregation tree specific to each branch (class of Products: level 4 of the official CPA nomenclature). Finally, the price indices of the branches are combined in order to obtain aggregates.

The aggregate indices (product classes at the CPA 4 digits level and above) are chain-linked Laspeyres indices, annually in reference to the base year. This means that the weights used to aggregate monthly price developments are updated once a year from the most recent sources of national accounts, structural business statistics and customs data, generally covering the year N-2.

The indices of the branches and of lower levels, although calculated according to the same formulas, are fixed base Laspeyres indices, because the weights are generally refreshed only when the representative transactions of the sub-samples concerned are renewed.

The operation associates professional unions, companies and INSEE. The companies surveyed in a branch are sampled at regular intervals (in principle once every five years) from the sampling bases available to INSEE.