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Subject Predicate Object <p>From now on, Industrial production indices have reference year 2015, which means that they have for average 100 in 2015. Previously, indices had reference year 2010.<br />The 2015 rebasing implements an important innovation, with the introduction of annually chained indices instead of fixed-weights indices. Thus, until now, aggregation of elementary indices was done on the basis of constant weights representing the reference year &ndash; i.e. 2010 previously. This method could lead to increasing distortions for the most distant&nbsp; periods from the base year. In order to reduce those distortions, the UN and Eurostat recommend to update weights annually. It is then necessary to link the indices from one year to the next, hence the final name. Three commonly used methods for chain-linking were studied in the context of the Eurostat "Chain-linking" task force. INSEE chose the annual overlap method for calculating the IPI.<br />Other indices, such as "production price indices", already used this type of annual chaining. Coherence between the IPI and structural statistics &ndash; including national accounts &ndash; is strengthened, although gaps remain due to differences in the data sources and calculation methods.<br />The estimation of annual weights is based primarily on the gross value added at basic prices per branch calculated by the annual national accounts. By definition, value added at basic prices excludes taxes on products but includes subsidies on products. It does not include transport services. At the lower levels of the industry classification, weights are also based on INSEE&rsquo;s Esane device and the Annual Production Survey in the industry.<br />Finally, from 2019, the IPI industrial branches will be reviewed at the rate of one fifth of the series each year. This annual update will make it possible to improve the relevance of the IPI with regards to the evolution of technologies and production processes, by including emerging products or, on the contrary, removing old products. This reviewing process of the products surveyed for the IPI was until now done every five years; the last update took place in 2013.</p>