How does Gallup decide how to “allocate” undecided voters?
The allocation procedure is a Gallup tradition, and represents Gallup scientists’ best estimate of what the final popular vote will be on Election Day.Here’s how it works. The unallocated numbers in the pool of likely voters (that is, the percentages of likely voters supporting Bush and Kerry, not including undecided voters) are 49% for Bush and 47% for Kerry. We assume, based on an analysis of previous presidential and other elections, that there is a high probability that the challenger (in an incumbent race) will receive a higher percentage of the popular vote than he did in the last pre-election poll, while there is a high probability that the incumbent will maintain his share of the vote without any increase. This has been dubbed the “challenger rule.” There are various explanations for why this may occur, including the theory that any voter who maintains that he or she is undecided about voting for a well-known incumbent this late in the game is probably leaning toward voting for
