Weighting
Stats SA publishes the RPPI at two levels of detail. Firstly, RPPIs for each province are aggregated to the 'national' RPPI. Secondly, the RPPIs for each of the eight metropolitan municipalities are aggregated to the 'all metropolitan areas' RPPI. Elementary indices are calculated for each metropolitan area and for the larger municipalities in each province. The hedonic model performs better if there are a large number of transactions available. Because there are fewer transactions each month for the non-metropolitan municipalities, their indices are not published.
The total sales value for any year can be calculated from the Deeds office data and this is used to aggregate the indices from the elementary level upwards. Aggregated indices for each year are weighted according to the total sales value of two years prior. For example, the results for 2022 are weighted based on the sales value of 2020, the results for 2021 are weighted based on the sales values of 2019, and so on. Weights will be updated annually with effect from the January RPPI each year.