It’s been an unpredictable year so far. (See Trump, Donald.) But the general election is off to a predictable start. Three Quinnipiac polls released on Tuesday, showing Donald Trump and Hillary Clinton neck and neck in Florida, Ohio and Pennsylvania, got far more attention than they deserved. That’s not because Trump can’t win those states, or the election. Rather, we’re still six months from Election Day and no single poll should receive much attention. Moreover, I would caution against getting bogged down in state polls — even of swing states. The truth is — with some notable exceptions — winning the national popular vote typically means winning the presidency; the Electoral College matters only in very close elections, and most of the time not even then.
1. The chance of an Electoral College and popular vote split is small.
Pundits love talking about scenarios in which one candidate wins the Electoral College and the other wins the popular vote. But like the fabled contested convention — it felt so close this year — such a split is usually more fantasy than reality. It’s happened just three times in the last 47 elections, going back to 1828 (by which point the vast majority of states began allocating their electoral votes by the winner of the popular vote in that state).1 Most elections simply aren’t all that close. During the past 50 years, for example, in only two elections has the national popular vote been within 2 percentage points.
And even in close elections, an Electoral College/popular vote split isn’t especially likely. Research by Nicholas R. Miller, a political scientist at the University of Maryland Baltimore County, has found that — all else being equal — there’s about a 25 percent chance of a split if the national popular vote is decided by about 1 percentage point, and that the chance is cut in half when the margin is 2 percentage points. We all remember the razor-thin margin in the 2000 election, when George W. Bush won the presidency even though Al Gore won the popular vote. But we forget that the 1960 and 1968 elections were about equally close but didn’t produce a split. Jimmy Carter in 1976 and George W. Bush in 2004 won relatively clear victories in the Electoral College while winning the popular vote by a little more than 2 points. If the national popular vote margin is greater than 4 percentage points, Miller found, the chance of a split is about zero.
Why are Electoral College/popular vote splits unlikely, even in tight races? Here’s one reason: Swing states aren’t swing states by accident. Especially in the aggregate, they tend to reflect the nation as a whole.
2. Without looking at all the states, we don’t know how to interpret state polls.
When incumbent presidents run for re-election, the electoral map tends to be fairly consistent with their first campaign. States that were competitive in 2008, for example, were also competitive in 2012 (with a couple of exceptions). Statistically, President Obama’s 2012 vote share in a state can be predicted within 4.5 percentage points, 95 percent of the time, just by knowing how much the national popular vote changed and how well Obama did in that state in 2008.2
But the map is far more likely to change in open elections, like 2016, when no incumbent president is running. In 2008, the state that voted most like the country overall was Virginia; Obama won the nation by 7.3 percentage points and Virginia by 6.3 points. Virginia also held that honor in 2012 — Obama won both the nation and the state by 3.9 percentage points. But in 2004, President George W. Bush won Virginia by over 8 percentage points while winning nationwide by a little less than 2.5 points. Nevada was actually the national bellwether in 2004, but Obama won it by double digits in 2008. Statistically, Obama’s vote share in 2008 could be predicted only within 6.4 percentage points, 95 percent of the time, based on 2004 state-by-state data.3 That error rate is nearly 2 percentage points higher than when Obama was running for re-election.
The point is that the 2012 electoral map may not apply in 2016. Let’s say Clinton leads Trump by 6 percentage points in North Carolina, as an average of the three polls conducted there in the past month suggests. So what? We don’t necessarily know what that says about the race overall.
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3. We don’t have a lot of state polls.
State polling is really good when we have a lot of it. That was one lesson of 2012, when the state polling in aggregate gave us a better picture of the national popular vote than the national polls did. And 2012 was not a fluke: State polls taken at the end of a campaign are often more telling than the national polls because there are lot more of them, among many different unique electorates.
But that math works only when you have a lot of state polling. From the first presidential debate last year in early October to Election Day, there were 126 polls taken in Florida, Ohio and Pennsylvania combined. According to HuffPost Pollster, only 96 national general-election polls were taken over the same period. In all of 2016 so far, we’ve had only 21 polls in these three states combined. That’s equal to the number of Clinton vs. Trump polls that have been conducted nationally in the last month.
The lack of state polling also potentially means individual polls receive more attention at a time when it’s hard to tell which surveys are outliers and which are real. You could get all worked up about the recent Quinnipiac poll that showed Trump within 1 percentage point of Clinton in Pennsylvania. But you’d be ignoring a recent Marist poll that had Clinton up 15 percentage points. With limited statewide polling data, we don’t know which is closer to the truth or whether whatever the truth is means anything for the national race at large.
You’re going to hear a lot about the Electoral College this cycle. At various points, one state or another will be declared pivotal. But stay calm, especially with so long to go until Election Day. It’s too early to take any poll too seriously. We’ll have plenty of time to get into the weeds of different Electoral College scenarios in the months to come. For now, if you’re interested in whether Trump or Clinton is likely to be our next president, I’d pay attention to the average of national polls. Let’s wait until we’re closer to the election and we have a lot more state polling before we zoom in closer than 30,000 feet.