How to factor in undecided voters to winning chances?

Question

If a 300 people well-conducted poll say:

• 35% Candidate A
• 5% Candidate B
• 60% Undecided

Can something be said about the winning chances of Candidate A? Is there a way to factor in the undecided statistically?

Answer 1

As long as there's no reason to assume that the 'undecided' group will show a different behaviour in the future, you could divide the votes in Undecided pro rata between options A and B. The estimated totals would then be:

• A: 35% + (60% x 35/40) = 87.5%
• B: 5% + (60% x 5/40) = 12.5%
• Undecided: 0, total 100%

Note that this is a very naive, numbers-only approach. If, for example, this poll was done before an election, and between the poll and the election one of the candidates rescues a three-legged puppy from a burning building, your mileage may vary.