Comparability of the harmonised indices
Article 4
1. For the harmonised indices to be considered comparable, any differences across Member States at all levels of detail shall only reflect differences in price changes or expenditure patterns. 2. Any sub-indices of the harmonised indices that deviate from the concepts or methods of this Regulation shall be deemed comparable if they result in an index that is estimated to differ systematically by: (a) less than or equal to 0,1 percentage points on average over one year against the previous year from an index compiled following the methodological approach of this Regulation, in the case of the HICP and the HICP-CT; (b) less than or equal to one percentage point on average over one year against the previous year from an index compiled following the methodological approach of this Regulation, in the case of the OOH price index and the HPI. Where the calculations referred to in the first subparagraph are not possible, Member States shall set out in detail the consequences of using a methodology which deviates from the concepts or methods of this Regulation. 3. The Commission shall be empowered to adopt delegated acts in accordance with Article 10 for the amendment of Annex I, in order to ensure comparability of the harmonised indices at international level in accordance with changes to the UN COICOP. 4. In order to ensure uniform conditions in producing comparable harmonised indices, and for the purposes of achieving the objectives of this Regulation, the Commission shall adopt implementing acts further specifying improved methods based on voluntary pilot studies as referred to in Article 8, and the methodology. Those implementing acts shall concern: (i) sampling and representativity; (ii) collection and treatment of prices; (iii) replacements and quality adjustment; (iv) index compilation; (v) revisions; (vi) special indices; (vii) treatment of products in specific areas. The Commission shall ensure that those implementing acts do not impose a significant additional burden on the Member States or on the respondents. Those implementing acts shall be adopted in accordance with the examination procedure referred to in Article 11(2). 5. With a view to the production of the harmonised indices, in order to take account of technical developments in the statistical methods and based on the evaluation of the pilot studies referred to in Article 8(4), the Commission shall be empowered to amend, by means of delegated acts adopted in accordance with Article 10, the first subparagraph of paragraph 4 of this Article by adding items to the list set out therein, provided that such added items do not overlap with existing ones and do not change the scope or nature of harmonised indices as set out in this Regulation.