The "Incumbent 50% Rule" says that an incumbent who stands at less than 50% in the final national polls is in deep trouble. Incumbents rarely get a higher result on election day than the pre-election polls indicate while the challenger usually does better. I've seen this phenomenon referred to previously but never so clearly stated as in this
piece by Guy Molyneux in The American Prospect.
So keep this in mind as you watch the polls over the next few weeks and make a wry smile every time you see one that puts Bush up by "x" with a 48% total.
Some extended excerpts:
However, in incumbent elections, the incumbent's percentage of the vote is a far better indicator of the state of the race than the spread. In fact, the percentage of the vote an incumbent president receives in surveys is an extraordinarily accurate predictor of the percentage he will receive on election day -- even though the survey results also include a pool of undecided voters. Hence the 50-percent rule: An incumbent who fails to poll above 50 percent is in grave jeopardy of losing his job.
But is it really possible for Kerry to close a 5-point gap, absent some fundamental change in voter preference? To find historical precedent, we must reach back in history all the way to 1996, the most recent incumbent presidential election. Bill Clinton averaged 51 percent in the final polls but received 49 percent on election day, while Bob Dole averaged 37 percent but received 41 percent -- a net shift of 6 points. Not only can Kerry close such a gap, it is extremely likely that he will.
Year Incumbent Final Polls Actual Vote
1996 Bill Clinton 51 49
1992 George Bush Sr 37 37
1984 Ronald Reagan 58 59
1980 Jimmy Carter 42 41
The numbers for challengers look quite different. In every case, the challenger(s) -- I include Ross Perot in 1992 and 1996 -- exceed their final poll result by at least 2 points, and the average gain is 4 points. In 1980, Ronald Reagan received 51 percent, fully 6 percentage points above his final poll results.