Economists do it with models, again

Updating my blog on Nate Silver's FiveThirtyEight.com model forecasts, I left the story in the aftermath of the RNC when it looked like any Romney bounce was below the expectations built into the model. Prior blog linked here.

The model is now responding to inputs from the DNC period, and is showing substantial gains in President Obama's probability of winning in the Electoral College. His probability as of today's (9/8/12) model update is 79.8%, up 2.5 percentage points since the end of the DNC, up 3.5 percentage points since the beginning of the DNC, up 8.2 percentage points since the end of the RNC, and up 10.5 percentage points since the beginning of the RNC. So the model has been consistently increasing the probability of an Obama win for the last 13 days. This is also a model high since it began in June. The early specific poll returns indicate that the Obama bounce is at or exceeding model expectations.

At an 80.0% probability of winning, Obama's win should be categorized as likely on the scale election forecasters appear to use.

I write these words, of course, with pleasure given my political bias. But also with fascination at the extent to which Nate Silver has gone to build a model which responds to the most important inputs to the eventual election outcome. Econometricians, good ones, rock!

This is a clumsy way to show the model output, but the site does not permit a link to just the graphs afaik. And I wanted to visually document the clear uptrend in Obama's winning probability as of this date.

Early Sunday update: Nate Silver has found faith in his model (it's OK Nate, you have the best model I am aware of): link here.

Election anti-bounce - economists do it with models

A very brief observation on economists, models, and the US presidential race.

Nate Silver, an economist (who successfully escaped the University of Chicago after completing his BA there), and a person who got hooked on econometrics, has the best electoral race forecasting model I am aware of.

During the 2008 race, he forecast the outcome within 0.1%.

His current model (as of 9/1/12) has President Obama's probability of winning at 72.0%. That is an increase of 2.7 percentage points during this last week of the Republican national convention. The Republican anti-bounce? Maybe they needed more of Dirty Harry, er, Clint Eastwood?

More importantly, this lead has been fairly consistent, perhaps slowly widening, since June. Those who call the race close are paying too much attention to the national horse-race polls. There, Obama's current projected lead is 1.8%, which is fairly close. But at this point has little bearing on the forecast outcome.

For the more wonkish of you out there, check out Nate's blog FiveThirtyEight.com here. Essentially, Nate's model is a (Bayesian?) weighted average of poll results and economic indicators. His results last time were impressive. It's the best political forecasting model I am aware of.

Update 9/3/12. Happy Labor Day! Some have suggested, including an anonymous comment here, that I am being too optimistic in interpreting the Silver models' outputs. No, I am interpreting the models' output. If they are trending toward Obama, that is what the model is saying.

So it is incumbent that if the model goes negative, I also report that output. Silver's Now-cast went negative early today, indicating a 3.1 percentage point decline from the intra-RNC peak to 71.0%. Note that level is 0.3 percentage points lower than the model indicated at the beginning of the RNC, so interpretation is sensitive to choice of starting points. Some, including Silver wearing his hyper-conservative hat, say this is evidence of a Romney RNC bounce.

OTOH, the paired Nov. 6 Forecast model, which has an adjustment for relative convention bounce as well as an adjustment for relative economic indicators, indicates a further widening in the probability of an Obama win, to 74.5%, a model high.

So the convention period was, in terms of these two models, a toss-up, or as Silver says a split-decision. No one knows which model is more accurate at this point in time; I simply point out that Silver built the Nov. 6 Forecast model to specifically adjust for relative convention performance. (Don't go too wobbly, Nate Silver). What is clear right now is that Romney has underperformed recent convention performances.

On to Charlotte to continue the saga.