“The Doctor Is In As Carson Ties Trump In GOP Race, Quinnipiac University National Poll Finds; Carson Tops Clinton By 10 Points In General Election”

That was the headline on a press release for the Quinnipiac University poll last week. My reaction? I hoped no one spent more than two seconds thinking about anything past the semi-colon. Since 1944, general election polls around a year before Election Day — where we are now — have only been weakly predictive of the eventual result.

If you look at polls that tested the eventual Democratic and Republican nominees in the last two months of the year before the election, the average absolute error of the polling average is 10.6 percentage points. That’s more than five times Ben Carson’s current lead over Hillary Clinton in the Huffington Post/Pollster.com aggregate. As you can see in the table below, 12 of the 14 elections for which we have polling data featured an error greater than Carson’s edge.

POLLING ACCURACY A YEAR BEFORE THE ELECTION ELECTION AVERAGE GOP POLL LEAD GOP ELECTION MARGIN ABSOLUTE ERROR 1964 -50.3 -22.6 27.7 1992 +21.0 -5.6 26.1 1980 -15.5 +9.7 25.2 2000 +11.9 -0.5 12.4 1984 +7.2 +18.2 11.0 1988 +18.0 +7.7 10.3 2008 -0.3 -7.3 6.9 1956 +22.0 +15.4 6.6 1944 -14.0 -7.5 6.5 2004 +8.7 +2.5 6.2 1996 -13.0 -8.5 4.5 1960 +3.0 -0.2 3.2 2012 -2.8 -3.9 1.0 1948 -3.8 -4.5 0.7 Average 10.6

The largest year-out lead belonged to Lyndon Johnson over Barry Goldwater in the 1964 election. Johnson, in the wake of John F. Kennedy’s assassination, led Goldwater by an average of 50 percentage points. Goldwater did lose in a 23-percentage-point blowout, but that margin was still less than half that projected by the early polls.

If you trusted the polls in late 1991, you might have thought Bill Clinton was finished in the 1992 presidential election. George H.W. Bush was ahead of Clinton by 21 percentage points at the time; Bush was basking in sky-high approval ratings after the first Gulf War. But as the Gulf War triumph faded and the economy became the focus of the campaign, Clinton would gain in the polls and eventually overtake Bush.

We can go on and on through the list. Yes, the early polls foretold Dwight Eisenhower’s 15-percentage-point victory over Adlai Stevenson in the 1956 campaign, but they also had Jimmy Carter defeating Ronald Reagan by 16 percentage points in the 1980 election. The Iran hostage crisis initially boosted Carter’s standing, but that didn’t last, and Reagan won by 10 percentage points that November.

Paradoxically, the 1948 race between Harry Truman and Thomas Dewey — the most famous polling mishap in U.S. election history — was the one with smallest difference between the polls a year out and the eventual results. The polling average a year out had Truman leading by just under 4 percentage points, and he won by just over 4 percentage points. That’s far more accurate than polls taken within a month of the election that had Dewey ahead by a comfortable margin.

But what about elections without an incumbent president on the ballot, like 2016? For the four we have data on, not a single one had an error of less than 3.2 percentage points.

Most recently, Barack Obama and John McCain were tied a year before the 2008 election. At that point in the campaign, more people cared about foreign policy than domestic issues. That changed dramatically as the global financial system collapsed, and Obama went on to win by over 7 percentage points.

The 2008 campaign is a good cautionary tale: We just don’t know what the most important issue will be at this time next year. Further, as my colleague Nate Silver has pointed out, a year out, “we have (almost) no Idea what the economy will look like on Election Day.” And the state of the economy is highly correlated with election results. Moreover, voters weigh the most recent economic news most heavily.

The second most recent non-incumbent election featured an even larger polling error. George W. Bush had a 12-percentage-point advantage over Al Gore in the early polls for the 2000 election, but Gore went on to win the national popular vote by half a percentage point. What changed? Bush, then the Texas governor, burst onto the national scene with relatively little negative media scrutiny. But that scrutiny grew as the primary and general election campaign progressed. According to Gallup, Bush’s net favorability dropped from +43 percentage points in December 1999 to +16 percentage points on the eve of the election.

Like Bush in late 1999, most of the Republicans running in 2016 haven’t been on the national scene for that long. For all the GOP candidates except Jeb Bush and Donald Trump, at least one-third of adults do not know enough about them to form a favorable or unfavorable opinion. It isn’t difficult to imagine candidates’ popularity shifting dramatically as they become better known. And as the net favorability of the candidates change, how well they do against Clinton or another Democrat could change as well.

History’s lesson is clear: Don’t pay attention to general election polls a year before the election.

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