DailyKos found a fascinating challenge to the conventional wisdom that undecided voters on election day vote for the challenger over the incumbent by 2 to 1. The My Election Analysis weblog takes a look at polls and voting for presidential elections from this century and finds that undecided voters, whether undecided in the summer, in the month before, or even in the week before the election, do not tend to favor the challenger.
My Election Analysis: Whither The Undecideds: "The fact is, there's no compelling evidence for such a trend. Since the advent of modern polling in 1936, there have been 12 Presidential elections where an incumbent ran. The good folk at Gallup have provided us with nice trendline charts for each of these years, which summarize their polling results: 1936, 1940, 1944, 1948, 1956, 1964, 1972, 1976, 1980, 1984, 1992, and 1996."