Their study took data from nearly 2000 public opinion surveys and compared it to the policies that ended up becoming law. In other words, they compared what the public wanted to what the government actually did. What they found was extremely unsettling: The opinions of 90% of Americans have essentially no impact at all.
[0] https://act.represent.us/sign/problempoll-fba/https://www.vox.com/2016/5/9/11502464/gilens-page-oligarchy-...
E.g. In such a system, if a state has 50 seats and a party manages to win 24 of them (while the second place only wins 23 seats), that first party gets all 50 seats of representation.
[1] https://en.wikipedia.org/wiki/First-past-the-post_voting
To be fair: My comment is mostly focused upon "Western" parliments, which includes two geographically non-Western places: Australia and New Zealand! If you look at the constant dominance of the Liberal Democratic Party (LDP) in Japan... look _very_ closely... you realise there are many competing factions within the party. So LDP _acts_ like multiple parties and forces the Prime Minister to compromise to get things done. Not perfect, but many outsiders fail to understand this about the Japanese (national) political system.
They constantly fall short, even of the narrow interests of whatever their particular constituency is. But there's kind of a floor where we just throw up our hands and say "WELL THEY WERE VOTED IN"
Do our officials receive less psychic pressure? Does the Chinese government work harder to align the populous' desires with their actions?
Pretty fascinating rabbit holes.