I would have expected breathless overinterpretation of numbers from Politico, but I’m disappointed to see Nate Silver follow suit.  Once again, this shows that a little statistics and not much contextual knowledge can really send an analyst the wrong way.

The context is what, on other grounds, is a nice story by Molly Ball in Politico, comparing the partisan breakdown of early voting returns in a number of states.  The problem is what Ball does with the numbers–and her error is compounded by Silver.

In both cases, they compare early voting turnout (NOTE: more than one week before election day–more on that later) to the overall registration figures in the state (Ball, Silver) and the party ID breakdown in the state (Silver).

This is then used as evidence of an enthusiasm gap.

You’d think they’d have learned.  A week ago, I chided Michael McDonald for pointing to “tantalizing” early voting numbers that showed just the opposite–no enthusiasm “gap” at all.  At the time, I noted that interpreting early voting numbers in a small number of states, and based on a small percentage of the eventual voters–was fraught with peril.

Now the national media have gotten in on the game.  A few important things to note about early voting turnout numbers at this stage in the game:

1) There are two ways to cast an early ballot, by mail (no excuse absentee) and in person.  The problem is that Ball and Silver lump the two together, even though we have long known that GOP voters tend (for reasons not well understood) to cast far more of their early votes as no-excuse absentee.

2) Among the states for which Ball is able to get data, virtually all are states where most early votes are no-excuse absentee votes (CA, CO, IA, LA, NJ, NV, OR, PA).

3) If history is any guide well under 50% of the “early” votes will be cast at this point, and in many cases we have examined in the past, less than 1/4 of the early ballots will be cast one week before the election.

In short, both Ball and Silver have “discovered” that Republicans mail in absentee ballots.  Congratulations!  Talk to me this Friday and Saturday, when early IN PERSON balloting has really opened, and we have more than 10% of the ballots cast.