Tax cuts for the wealthy have long drawn support from conservative lawmakers and economists who argue that such measures will "trickle down" and eventually boost jobs and incomes for everyone else. But a new study from the London School of Economics says 50 years of such tax cuts have only helped one group — the rich.

The new paper, by David Hope of the London School of Economics and Julian Limberg of King's College London, examines 18 developed countries — from Australia to the United States — over a 50-year period from 1965 to 2015. The study compared countries that passed tax cuts in a specific year, such as the U.S. in 1982 when President Ronald Reagan slashed taxes on the wealthy, with those that didn't, and then examined their economic outcomes.

Per capita gross domestic product and unemployment rates were nearly identical after five years in countries that slashed taxes on the rich and in those that didn't, the study found.

But the analysis discovered one major change: The incomes of the rich grew much faster in countries where tax rates were lowered. Instead of trickling down to the middle class, tax cuts for the rich may not accomplish much more than help the rich keep more of their riches and exacerbate income inequality, the research indicates.