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Subject Predicate Object <p>The calculation of industry price indices is harmonized within the European Union and led to the publication of a methodological manual in 2012.</p> <p>The industry price indices measure trends in prices, not seasonally adjusted. Price series in level are immediately converted into indice series, and then aggregated according to an aggregation tree for each activity (a activity corresponds to a product of the CPF4 official nomenclature). Finally, the price indices of the different activities are combined to obtain aggregates defined at higher levels (CPF3, CPF2 and total of the Industry).<br /> Aggregated indices are Laspeyres chain-linked indices, annually referenced in 2015, that is to say that the average value in 2015 of Production price indices and import price indices in Industry is 100.</p> <p>Weights used to aggregate the monthly price evolutions are updated once a year, in May in order to calculate the definitive value of the indices for January. These  weights come from different sources : national accounts, structural business statistics and customs data.  The latest available data are used, usually on the year N-2. activity Indices and those calculated at lower levels are fixed basis Laspeyres indices. Their weights are usually updated only during the renewal of the samples of the survey for the activity concerned. The companies, the sample transactions, and weights (turnovers or amounts of the company's imports for the products tracked) are then updated.</p>