In August 2009, REINZ began publishing a stratified housing price index, which is based on the same data, but uses mix-adjustment to adjust for compositional change. The index is calculated back to January 1992, the first month for which electronic information is available. The approach used to calculate REINZ’s housing price index is very similar to that outlined in the Reserve Bank of New Zealand’s discussion paper Developing Stratified House price measurement in NewZealand. Housing Price Measures for New Zealand (McDonald & Smith, 2009). However, as further improvement, the REINZ housing price index is now calculated using sales for all transactions (rather than the median price for each suburb) within the stratum.