... To tell these various scenarios apart, we need to analyse to what extent top tax rate cuts lead to higher economic growth. Figure 2 shows that there is no correlation between cuts in top tax rates and average annual real GDP-per-capita growth since the 1970s. For example, countries that made large cuts in top tax rates such as the United Kingdom or the United States have not grown significantly faster than countries that did not, such as Germany or Denmark. Hence, a substantial fraction of the response of pre-tax top incomes to top tax rates documented in Figure 1 may be due to increased rent-seeking at the top rather than increased productive effort.
Naturally, cross-country comparisons are bound to be fragile, and the exact results vary with the specification, years, and countries. But by and large, the bottom line is that rich countries have all grown at roughly the same rate over the past 30 years – in spite of huge variations in tax policies. Using our model and mid-range parameter values where the response of top earners to top tax rate cuts is due in part to increased rent-seeking behaviour and in part to increased productive work, we find that the top tax rate could potentially be set as high as 83% – as opposed to 57% in the pure supply-side model....