There’s a very large gulf between my conclusion, explained on Friday, that Obama is toast on Election Day and confident projections like Nate Silver’s poll-reading model still giving the president (at last check) a 77.4% chance of victory. Let me explain why, and what that says about the difference between my approach and Nate’s.
The Limits of Mathematical Models
“A page of history is worth a volume of logic” – Oliver Wendell Holmes
Mathematical models are all the rage these days, but you need to start with the most basic of facts: a model is only as good as the underlying data, and that data comes in two varieties: (1) actual raw data about the current and recent past, and (2) historical evidence from which the future is projected from the raw data, on the assumption that the future will behave like the past. Consider the models under closest scrutiny right now: weather models such as hurricane models. These are the best kind of model, in the sense that the raw data is derived from intensive real-time observation and the historical data is derived from a huge number of observations and thus not dependent on a tiny and potentially unrepresentative sample.
Yet, as you watch any storm develop, you see its projected path change, sometimes dramatically. Why? Because the models are highly sensitive to changes in raw data, and because storms are dynamic systems: their path follows a certain logic, but does not track a wholly predictable trajectory. The constant adjustments made to weather models ought to give us a little more humility in dealing with models that suffer from greater flaws in raw data observations, smaller sample sizes in their bases of historical data, or that purport to explain even more complex or dynamic systems – models like climate modeling, financial market forecasts, economic and budgetary forecasting, or the behavior of voters. Yet somehow, liberals in particular seem so enamored of such models that they decry any skepticism of their projections as a “War on Objectivity,” in the words of Paul Krugman. Conservatives get labeled “climate deniers” or “poll deniers” (by the likes of Tom Jensen of PPP, Markos Moulitsas, Jonathan Chait and the American Prospect) or, in the case of disagreeing with budgetary forecasts that aren’t really even forecasts, “liars.” But if history teaches us anything, it’s that the more abuse that’s directed towards skeptics, the greater the need for someone to play Socrates.