A story in the Telegraph of London (which explains some of the spelling), says the study shows that "the central point ... is that economic elites and organised groups representing business interests have substantial independent impacts on U.S. government policy, while mass-based interest groups and average citizens have little or no independent influence."
The report is called Testing Theories of American Politics: Elites, Interest Groups, and Average Citizens, and is based upon data collected between1981 and 2002. Researchers went through about 1,800 U.S. policies enacted in that period "and compared them to the expressed preferences of average Americans (50th percentile of income), affluent Americans (90th percentile) and large special interests groups, researchers concluded that the United States is dominated by its economic elite."
The study found that "government policies rarely align with the the preferences of the majority of Americans, but do favour special interests and lobbying oragnisations: 'When a majority of citizens disagrees with economic elites and/or with organised interests, they generally lose. Moreover, because of the strong status quo bias built into the U.S. political system, even when fairly large majorities of Americans favour policy change, they generally do not get it."
There has been a debate for many years about whether the U.S. is a republic ("in which power is exercised by the public at large") or a democracy ("a system involving distribution of political power in the hands of the public which forms the electorate, representative government"). I don't see much evidence it's ever been either. Oligarcy ("government by the few") is close to right these days. And it's moving toward feudalism ("a set of reciprocal legal and military obligations among the warrior nobility, revolving around the three key concepts of lords, vassals and fiefs"; that would be the Koch brothers, Congress, us).