Half of Americans agree with Trump's 'poisoning the blood' immigration rhetoric

[Ocelot II]

8. You Gov surveys depend on people responding to them, not on random calls

like most polls. I'm on their list, too, and I respond for the same reason - Amazon gift cards. I have no idea how they can quantify their overall accuracy. For political surveys they always ask whether you're a Dem, GOPer, Independent, whether, e.g., you're a strong Dem, whether you voted in the last election, who you voted for, who you intend to vote for, etc., but they can only count up the percentages in the total responses. How do they determine whether and to what extent those responses reflect any national trends?