This hypothesis was formalized in the context of a Solow model by Bourguignon (1981) who showed that when savings are a convex function of income, there may exist multiple steady states characterized by different degrees of inequality. Another possibility, however, is that they end up eliminating most of the variation in the data, exacerbating measurement error biases and reflecting in practice only the short-run effects of inequality. But many of the theoretical effects of inequality on growth may take a significant amount of time to materialise (changes in education, or in political stability, for example).