The development of purchasing power parities as converters of national accounts aggregates to comparable volume figures is important for international economic comparisons. This study is primarily concerned with the aggregation of price relativities to basic heading level: that is, the level below which there are no expenditure weights available across all of a given group of countries. Eight possible methods of aggregation to basic heading level are identified and appropriate summary statistics developed to assist in the subsequent practical investigation of these methods. This is undertaken using price data for 37 basic headings in ten OECD countries ...