Preelection polls jump all over the place. …
Polls fluctuate, and when the latest poll is much different from what came before, we’re likely to see a bounce back — not because of any deep political forces, but just because what we’re seeing is a sequence of noisy measurements.
We should care about this because it’s all too easy to launch into a new story for each poll: Hillary’s up because she did this, she’s down because she did that, and so forth. But if we try to explain each roll of the dice, we’re overexplaining — and, ultimately, explaining nothing. CONT.
Andrew Gelman (Columbia), The Monkey Cage