Forecasting the Presidential Election: Is it Wise to Bet Against Nate Silver?

In today’s New York Times Nate Silver establishes President Obama as a prohibitive favorite in Tuesday’s electoral vote contest.  His projection is based largely on the information in state polls in key swing states.  While national polls suggest that the popular vote total will be close, Silver’s simulations indicate that President Obama has an 85% chance of winning re-election on Tuesday.  Silver’s projections, which have come under attack from Romney supporters in recent weeks, rely on a combination of state, national and tracking polls.  His state-by-state forecasts use a sophisticated algorithm to weight information based on the accuracy of previous polls, the number of undecided voters in each state, and recent trends.

I have no doubt that the President is the favorite to win re-election on Tuesday because Mitt Romney needs to win the vast majority of swing states in order to reach 270 electoral votes.  Silver, a successful former poker player, has established Mitt Romney as an 11:2 longshot.  Given the closeness of the national polls it may seem tempting to some to question Silver’s forecast.  Could Silver possibly be wrong?  The answer rests with his reliance on state polls, and the accuracy of state polls in swing states where the races are fairly close.

In today’s column Silver makes a convincing case that state polls are accurate, on average, especially as we get close to election day.  He states:

“Of the 77 states with at least three late polls [since 1988], the winner was called correctly in 74 cases …There has been little tendency for the state polling averages to overrate either Democrats or Republicans, or either incumbents or challengers.”

I examine only the 60 state poll averages since 2000 listed by Silver (and ignore the small group of state polls he lists from 1988-1996).  Silver is correct that state polls are correct, on average.  The average difference between the election outcome and the late poll in a state is about one-quarter of one percentage point.  Nonetheless, state polls tend to lean one way in one election and another way in a different election.  In 2000, Al Gore outperformed state poll projections by an average of 2.14 percentage points.  In 2004 George W. Bush outperformed state poll projections by an average of 1.52 percentage points, a swing of 3.66 percentage points in just 4 years.  In addition, John McCain outperformed state polls by 0.70 percentage points in 2008.  If the prediction error in state polls was truly independent of all factors, we would only expect to see such large differences in average prediction errors across elections less than one time in three hundred (less than once every millennium).

What does it mean that state polls lean in different directions from election-to-election?  As a practical matter it means that once we observe the difference between actual election outcomes and late state polls in a state such as New Hampshire on Tuesday, we will have a better idea what will actually happen in Florida, Ohio, Virginia and other swing states.  In the language of statistics the forecast errors from polls are correlated among states in the same election cycle.  These correlations within the same election cycle mean that the candidate that exceeds expectations in one state is likely to exceed expectations in other states as well.

State polls are clearly missing something that varies from election-to-election.  I have no idea whether the late state polls in 2012 will miss the forecast because of turnout, momentum, the political preferences of late deciders or how voters who refuse to answer pollsters will actually cast their ballots.  I am also not sure whether the forecast errors will favor the President or Mitt Romney.  What does seem plausible, however, is that the difference between late state polls and actual vote totals will be more than one-quarter of a percentage point, the overall average since 2000.

When Silver establishes the President as an overwhelming favorite it is based on a model that has been estimated over a relatively small number of situations in recent elections where the race was expected to be close at the state level.  The projected margin of victory/loss in state poll averages was within 6 percentage points only 28 times in the three presidential elections from 2000 to 2008.  To statisticians, that is a fairly small sample.  But more importantly, when one state poll tends to underestimate the strength of a candidate, whether Democrat or Republican, other state polls tend to make the same mistake.  Silver’s forecast is betting that state polls will be very accurate in 2012, which is different from saying they have been accurate, on average, across several elections.  So if you see Nate Silver and he offers you 11:2 odds on a bet that Mitt Romney wins the election, you might want to take it.  But be careful of his poker face.

George McGovern: Why Presidential Candidates Should Have a Business Background

Nick Gillespie, editor in chief of of Reason.com, has written an excellent tribute to George McGovern on Bloomberg View.  Gillespie explains McGovern’s libertarian approach to foreign policy interventions but what interested me most was his explanation of McGovern’s evolution on domestic policy, especially regulatory overkill.  After leaving politics Senator McGovern became a small business owner – the proprietor of a Connecticut inn.  In a June 1, 1992 opinion piece for the Wall Street Journal entitled “A Politician’s Dream is a Businessman’s Nightmare” McGovern described how a “severe” recession and government regulations at the federal, state and local levels crippled his small business.  McGovern’s editorial also revealed his belief that a prior background in business is helpful for a presidential candidate:

I also wish that during the years I was in public office, I had had this firsthand experience about the difficulties business people face every day. That knowledge would have made me a better U.S. senator and a more understanding presidential contender.

McGovern explained that politicians with no background in business have a naive view that regulations either impose no costs on businesses or that these costs can easily be shifted to customers or workers.  In the editorial he wrote:

the concept that most often eludes legislators is: `Can we make consumers pay the higher prices for the increased operating costs that accompany public regulation and government reporting requirements with reams of red tape.’  It is a simple concern that is nonetheless often ignored by legislators.

It is also revealing that perhaps the most liberal Democratic presidential candidate in history was hopeful that the Democratic party of 1992 was headed in a different direction – a direction to encourage business formation and capital investment:

Today we are much closer to a general acknowledgment that government must encourage business to expand and grow. Bill Clinton, Paul Tsongas, Bob Kerrey and others have, I believe, changed the debate of our party. We intuitively know that to create job opportunities we need entrepreneurs who will risk their capital against an expected payoff. Too often, however, public policy does not consider whether we are choking off those opportunities.

These words of wisdom from a great American and liberal icon are as important today as when Senator McGovern wrote them 20 years ago.

Forward?

I am not a political consultant, but if I worked for President Obama’s re-election campaign I would be concerned about the impression commuters in northern Virginia might be forming about the campaign’s “Forward” slogan.  “Forward” is also the slogan used by the Washington Metropolitan Area Transit Authority (WMATA) to explain why it is taking so long to repair the escalators at WMATA stations.  The sign on an escalator at the Rosslyn station pictured above indicates that it will take from July to October to repair.  To some commuters the unreliable escalators in Metro stations, and the length of time it takes to repair them, may symbolize inefficient and wasteful government spending.

The connection between public investment in projects like WMATA escalators and President Obama’s reelection campaign was reinforced when the President told us that successful small business owners and entrepreneurs owe credit for some of their success to public investment in transportation infrastructure.  Recall that one month ago today in Roanoke, Virginia, President Obama said:

If you were successful, somebody along the line gave you some help…. Somebody invested in roads and bridges.  If you’ve got a business — you didn’t build that.  Somebody else made that happen.

There is no doubt that many transportation infrastructure projects have benefits that far outweigh their costs and require both public and private investments.  Other projects, promoted by politicians from both parties, are laden with political pork.  Still others, like WMATA escalators, are valuable to the community but seem to be completed at a glacial pace (and probably exorbitant cost).

Virginia is an important swing state, and the President must do well among independent voters in northern Virginia to carry the state.  I suspect that few of the independent voters credit much of their professional success to the efficiency of WMATA.  The President is correct in saying that these independent voters didn’t build the Metro system or its escalators, but they are also not responsible for the system’s inefficiencies and state of disrepair.