The quantile ratio index is a simple and effective measure of relative inequality for income data that is resistant to outliers. A useful property of this index is investigated here: given a partition of the income distribution into a union of sets of symmetric quantiles, one can find the inequality for each set and readily combine them in a weighted average to obtain the index for the entire population. When applied to data for various years, one can track how these contributions to inequality

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... vary over time, as illustrated here for Australian Bureau of Statistics income and wealth data.