Contradictory trends in global income inequality: A tale of two biases

Did global income inequality rise or fall over the last decades of the twentieth century? The answer depends on how cross-country income comparisons are made. Exchange rate comparisons suggest that inequality rose whilst the purchasing power comparisons of the Penn World Table suggest it fell. We show that both measures of real incomes lead to biased international income comparisons. Exchange rate comparisons ignore the relative price of non-tradables, whilst the fixed price method underlying the Penn World Table is subject to substitution bias. The contradictory trends are due to growing dissimilarity between national price structures increasing the degree of bias in each method. When we correct the income data to eliminate bias we find no compelling evidence of a significant change in world inequality.