She’s up! She’s down! He’s closing! He’s fading.
Nate Cohn at the NYT does a truly fantastic job of laying out yet another reason why shifts in the polls don’t mean what people seem to think they mean. It’s all a function of normal distributions and bell curves, and in many ways it’s just like baseball, but with one HUGE exception: there’s only one game day in politics – Election Day – so polling streaks are entirely meaningless until and unless they represent a fundamental change in expected voter behavior. Nate explains:
If Mrs. Clinton leads by 4 points, you should expect polls that show her with a big lead or locked in a tight race, with others clustered around the average. That’s more or less what we saw this past week. It’s a lot like baseball. Even great baseball players go 0 for 4 in a game — or have rough stretches for weeks on end. On the other end might be a few multihit nights with extra-base hits, or a spectacular few weeks. Sometimes, these rough stretches or hot streaks really do indicate changes in the underlying ability of a player. More often, they are just part of the noise inevitable with small samples. Taking more polls is like watching more at-bats, and you need many if you want to be confident about whether a candidate is ahead or tied.