of the change in RPI, due to fluctuations in mortgage interest rates, is shown in the graph on the right. This was one of the arguments used in favour of changing to RPIX. Variations Variations on the RPI include the RPIX, which removes the cost of mortgage interest payments, the RPIY, which excludes indirect taxes (VAT) and local authority taxes as well as mortgage interest payments, and the RPIJ which uses the Jevons (geometric) rather than the Carli (arithmetic) method of averaging. See also Consumer price index (general concept) Price index (more detailed statistical explanation) References External links Consumer Price Indices: A brief guide, Office for National Statistics, 2013 Retail Prices Index topic page at ONS website Price indices Economy of the United Kingdom Office for National Statistics 1947 introductions Inflation in the United Kingdom