This is some absolutely crazy data. In summary, black and poor people advocating for a policy results in a slightly lower chance of it being enacted. For women, advocating for a policy means it is significantly less likely to be enacted. It is important to note, this data only shows a correlation, so the reasons are purely speculative, but this is really depressing to see.
Also relevant: http://www.bbc.com/news/blogs-echochambers-27074746
So concludes a recent study by Princeton University Prof Martin Gilens and Northwestern University Prof Benjamin I Page.
This is not news, you say.
Perhaps, but the two professors have conducted exhaustive research to try to present data-driven support for this conclusion. Here's how they explain it:
Multivariate analysis indicates that economic elites and organised groups representing business interests have substantial independent impacts on US government policy, while average citizens and mass-based interest groups have little or no independent influence.
In English: the wealthy few move policy, while the average American has little power.
Chomsky mentioned this many times before, here for example.