Political innumeracy

A couple of quick pre-election notes:


1. If I could outlaw one type of political journalism, it’d be stories of the form “This election will be decided by voters of Type X” (Rural voters, working-class voters, etc.) In past elections, we were told that the election would be decided by soccer moms, NASCAR dads, security moms, and a host of others.

The problem with these statements is not that they’re false — it’s that they’re true but vacuous. What does it mean to say that the election will be decided by young, unmarried women? It means that, if young, unmarried women tend to vote more than expected for a candidate, then that candidate will win. But in a close election, that’s equally true for all groups.

The problem is that “if more people vote for your guy than the other guy, then your guy will win” doesn’t make for a compelling campaign narrative, so the poor beleaguered horserace journalist has to come up with some novel-sounding theory about some particular group that’s going to “decide” the election. Either that or they could find something useful and important to write about.


2. One bit of good news from the campaign: Bayesian reasoning has gone mainstream. Look at all the attention Nate Silver‘s been getting.

It won’t surprise anyone who knows me to hear that I love Silver’s approach to political analysis. I’ll take a clear model built on data over 100 pundits’ gut feelings.

A number of Republican-leaning types hate Silver, because his model consistently says Obama’s more likely to win. It’s true that Silver is openly pro-Obama, and it’s true that people have a tendency to (consciously or unconsciously) skew things in the direction they prefer. But there are several reasons one shouldn’t make too much of this argument:

  • Other quantitative, statistics-based models give predictions similar to Silver’s or even more pro-Obama, as do the betting markets. See, for example, the Princeton Election Consortium.
  • Silver’s reputation as a prediction whiz is on the line. His motivation to be accurate is probably stronger than his motivation to boost his guy.
  • Silver laid out his methodology explicitly and publicly quite early on, and as far as I know there’s no evidence he’s changed it.

Of course, Silver’s model might be wrong nonetheless. Some people have said silly things like “We’ll know next week how good his model was,” but of course we won’t. As Ezra Klein put it,

If Mitt Romney wins on election day, it doesn’t mean Silver’s model was wrong. After all, the model has been fluctuating between giving Romney a 25 percent and 40 percent chance of winning the election. That’s a pretty good chance! If you told me I had a 35 percent chance of winning a million dollars tomorrow, I’d be excited. And if I won the money, I wouldn’t turn around and tell you your information was wrong. I’d still have no evidence I’d ever had anything more than a 35 percent chance.

One of the sillier critiques of Silver came from Josh Gerstein of Politico:

Isn’t the basic problem with the Nate Silver prediction in question, and the critique, that it puts a percentage on a one-off event?

Of course we use probabilities to describe one-off events all the time. Does Gerstein listen to weather forecasts?

Then there’s the New York Times’s public editor, Margaret Sullivan, who thinks Silver violated journalistic ethics when he offered to make a bet against Joe Scarborough. Scarborough insists that anyone who thinks the race is anything other than a tossup is an idiot, so Silver offered him an even-money bet on the race (with the loser donating money to charity, so neither stands to gain personally).

Sullivan’s point of view on this strikes me as extremely silly. Offering to bet is a standard rhetorical trick when having arguments about probabilities. If you really believe in your probabilistic statement, you should be willing to use it as the basis of a bet.

I don’t think I’ve ever used vulgar language in this blog before, but here goes: by far the best way to put this point is Alex Tabarrok’s line : A bet is a tax on bullshit. If all pundits who opine about the race had to put bets on their predictions, we’d be a lot better off.


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Ted Bunn

I am chair of the physics department at the University of Richmond. In addition to teaching a variety of undergraduate physics courses, I work on a variety of research projects in cosmology, the study of the origin, structure, and evolution of the Universe. University of Richmond undergraduates are involved in all aspects of this research. If you want to know more about my research, ask me!

5 thoughts on “Political innumeracy”

  1. Ted, agree with all the above but would also add one point. Pundits often tend to overestimate the impotance of independent voters vis-vis turnout of the base. A lot of Obama’s lead comes from Democrats’ advantage in voter registration, so if they turn out in sufficient numbers he’ll win even if the independents break more for Romney.

  2. I didn’t follow the corresponding link on the editor who believes Nate Silver violated journalistic ethics, but many of the publishing practices of the so-called “mainstream media” violate my own concept of journalistic ethics, specifically the concept of newsworthiness. The New York Times is no fish wrap of course, but they and probably all major outlets are guilty of printing junk that doesn’t matter, not because the story needs to be told but because folks will pay attention to the story and hopefully any ads which happened to be lying around.

    I’m mostly unfamiliar with the ins and outs of Nate Silver’s stuff, but I have read about some of his prediction results and it’s very interesting. I’m all for someone who analyzes a popular question using such techniques, even if he bets on it to make his point and — God forbid — whose techniques require more critical thinking than one calls on in the 5 minutes required to read a gimmicky op-ed.

    With that sad, there’s a fine chance that editor is an extremely ethical person who wouldn’t be associated with the stuff I mentioned, in which case the reader has just wasted time reading *my* opinion!

  3. Really, all of this is moot as long as the US a) has a highly non-linear electoral system in which one can (even legally—not the hanging-chad stuff) win even if the other guy has more votes and b) say that it is the best system in the world. The sad thing is that most people don’t even understand this. One guy wrote “Well, that might be true but if it ever happens that someone gets the majority of the popular vote but doesn’t win, things will change” then someone pointed out that a) this has already happened and b) not many people knew or cared.

  4. Although we won’t know, in the macro sense, whether Silver’s model was accurate, the basic components of the model should be susceptible to extensive analysis. I would think that we’ll see quite a bit of deconstruction and analysis from Silver over the next few months about the accuracy of the state-specific vote shares that he publishes, along with the inputs and the methodology for turning that into his top-line percentage.

    I think Sullivan’s articles showed her lack of understanding of Silver’s work – he’s not a pundit or reporter in the traditional sense and his offered wager was a bet on his model not the candidate. That said, it seems like a slightly off-key wager to resolve “The race is a toss-up.” vs. “No, it isn’t.” Silver has done much better over the past few days to just use his column as a bully pulpit:

    “Nevertheless, these arguments are potentially more intellectually coherent than the ones that propose that the leader in the race is “too close to call.” It isn’t. If the state polls are right, then Mr. Obama will win the Electoral College. If you can’t acknowledge that after a day when Mr. Obama leads 19 out of 20 swing-state polls, then you should abandon the pretense that your goal is to inform rather than entertain the public.”

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