Consider the complications

One of the many things I like about Nate Silver's approach to interpreting numbers is that he takes the time to explain his methodology clearly, supports his decisions, and sets out the advantages and disadvantages of his choices. One example is last week's column titled "Why is Santorum Overperforming his Poll Numbers?"

As Silver puts it:

The FiveThirtyEight forecast model is based on statewide polls and statewide polls alone in presidential primaries and caucuses. It doesn’t do anything especially fancy. This approach has advantages and disadvantages.
The disadvantage is that if the polls are wrong, the model will be wrong too. . . 

The advantage is that the model gives us a relatively clean and objective benchmark to evaluate the candidates’ actual performance against the polls.

He then compares his model against Santorum's performance in the states with robust polling, and in states with limited polling, and concludes that Santorum has outperformed the polls by a small amount - 2.3 percentage points in the smaller set, and 2.1 percentage points in the larger set, enough to be statistically significant. Silver offers fours hypothesis (higher Santorum turnout, neglect of cellphone-only voters, unwillingness to reveal choices to poll takers, and tactical voting) that might explain the difference, and considers each of them in turn.

It's a good piece, clearly written. It enlarges our understanding of what's happening.  (And in case you're wondering, Silver thinks Santorum is unlikely to get the nomination.) Because it continues the conversation as events develop, this kind of iterative approach is a good model to follow for anyone who has to explain numbers for a living.

It's an election year! Time to start obsessing about polling

Let's start with Presidential approval ratings.

According to a CBS News poll released yesterday, President Obama's are up, reaching 50% for the first time since May, 2011:

CNN's polls say the same thing. So do Rasmussen Reports, which says that 49% approve of the President, and that 49% disapprove. They display the data differently:

What's going on here? I suspect it's in the way the questions are asked and the data tabulated. If CBS and CNN subtracted the lukewarm approvals from the strong approvals, you might get the 27% strong approvals that Rasmussen reports. But it appears that right now there are more people expressing strong and lukewarm approval than there are expressing disapproval. The takeaway? If you can, look at more than source for information. And think about how each organization is reporting its data. And right now, in a head-to-head competition, even Rasmussen reports that Obama beats Santorum and Romney.

Which is what Nate Silver, of FiveThirtyEight (now a part of the New York Times) reports as well. I should say that's what Silver concludes, as he is using an early stage model taking account of the economy, each candidate's ideology, and the approval ratings. He also has some projections about upcoming Republican primaries (in Arizona, Michigan, Georgia, and Ohio). FiveThirtyEight is a great site, and I'll be keeping an eye on it in the coming months. Even though the election is still nine months away.