How we know what we think we know: polling basics

Since the Democratic presidential primary contest and reactions to the Trump impeachment inquiry are both going to inspire feverish poll taking, it seems worthwhile to share here some basics of what these mathematical wizards do. They are not always right, but they are not just pulling the numbers in the media out of their asses either.

I like this from Pew which explains how talking with less than 1000 people can stand in for, and reveal reasonably accurately, the views of a country of nearly 330 million.
The clip is the introduction to a valuable series which explores the concepts and practices involved. I'll probably pass on some more of them during the 2020 election cycle.