Maybe you should have made clear in your post, then, that u is utility, not income. If u is utility and v is income, then v'(x)/v(x) ~ u'(x), more or less. Mo

Maybe you should have made clear in your post, then, that u is utility, not income. If u is utility and v is income, then v'(x)/v(x) ~ u'(x), more or less. Most measures of inequality involve dollar ratios, which seem to correspond to differences in utility, or at least to self-reported happiness.