The harmonised indices of consumer prices (CIP) are calculated in each member state of the European Union for the purpose of European comparisons. From January 1999 it has been used by the ECB as the measure of price stability cross the euro area. In comparison to RPI, CPI uses the geometric mean to aggregate the prices at the most basic level, RPI uses arithmetic means. A number of RPI series are excluded from HICP, including those relating to housing costs(eg council tax), and also owner occupiers' housing costs(eg mortgage interest payments, house depreciation, and buildings insurance). Coverage of CPI is based on the international classification system, COICOP(classification of individual consumption by purpose). Please note that inflation rates prior to 1997 and Index levels prior to 1996 are estimated. Please see ECST UK<GO> for further UK economic statistics, inclusing RPI and CPI breakdown.