Posted by Jay Livingston
Uncertainty and probability are really hard for people, even undergraduates in statistics classes, to understand. I mean, really understand – grok (do people still say “grok”?).
“The polls were wrong,” our president is fond of saying. “They said Hillary would win.” No. What the polls said is that the probability of Hillary winning was 65% (or whatever). That is, sixty-five percent of the time when we get poll results like these, Hillary will win. And 35% of the time, Trump will win. The result is uncertain.
In most of their reporting of results, the pollsters don’t emphasize or even explain the idea of probability. They hope that the people who read their reports will know what “65% probability” means. But they also know that most people, including political reporters, will reduce the message to, “Hillary’s gonna win.”
Maybe it would help if the pollsters included some boilerplate about probability and uncertainty – you know, down at the bottom of the page where they put the sample size and dates and margin of error. Nah. That probably wouldn’t help. It’s like Q-tips. That’s Ezra Klein’s a wonderful analogy. You can hear it in this clip from his recent conversation with Julia Galef. (The excerpt is four minutes long, but the Q-tips part starts at about 0:45. The rest is context and further explanation.)
Here’s an approximate transcript:
You know how on the packaging of Q-tips they say, “Please don’t put these in your ear”? And ... the only thing ... people do with them is buy them and then immediately stick them into their ear as far as they possibly can, because that’s what you use a Q-tip for. And the Q-tip company knows this perfectly well. What the political forecasters ... are saying is, “We’re giving you an accurate probabalistic forecast, and what you really need to understand is that this is fundamentally a tool to show you that there is uncertainty in elections. And what everybody is doing – and they know this perfectly well – is running to ... get certainty, to get the one thing that they’re told they’re not supposed to use this for. |
We can accept uncertainty and probability in other areas. Last night, ESPN broadcast the final round of the World Series of Poker. With only one card (“the river”) unseen, Ott’s Ace/8 would beat Blumstein’s Ace/2. The only way Blumstein can win is if a deuce turns up on the river. The screen (upper left) shows these three “outs” – the only cards that will help Blumstein. If any of the other 39 cards left in the deck turns up, Ott wins the 128,000,000 in the pot.
(Click on an image for a larger view.)
As ESPN showed, Ott’s probability of winning the hand is 93%. Blumstein has only a 7% chance. Most viewers – and certainly most poker players – knew what ESPN meant. ESPN was not saying “Ott’s gonna win.” It was saying that if the hand were played from this point 100 times, Blumstein would lose 93 times. But he would win 7 times. Seven times in hundred, he’d get the deuce.
You can guess what happened.
Nobody said, “ESPN got it wrong. Fake percentages. Never believe ESPN.”
We understand that poker is about uncertainty and probability. But we find it much harder to think this way about human behavior – voting for example. Suppose pollsters remind us that their polls show only probability. “We told you that tf the election were run 100 times, Hillary would lose 35 times.” My reaction is, “That’s ridiculous. The same people would vote the same way, so she’d lose every time. Voters are not cards – you don’t shuffle them up and then turn over one voter on the river.”
No. But that’s exactly what polls are – samples of the deck of voters. The results give us probabilities, not predictions. Unfortunately, most of the time, most of us ignore that distinction. And we stick Q-tips in our ears.