The Simple Math Behind The Power Of The Swing Vote

After the Democratic National Convention this week, and the official announcement of the Obama-Biden ticket, there’s been a lot of chatter about where Clinton supporters stand, regardless of the clear message of Clinton’s “No Way, No How, No McCain” speech at the DNC. The reason for the chatter? Analysts are trying to get a feel for what the true population of swing voters looks like. More than ever, parties are recognizing that their futures lie in winning at the center, rather than at the extremes, because the impact swing voters have on an election is so profound. The math behind the power of the swing vote is actually quite simple – In his book Microtrends: The Small Forces Behind Tomorrow’s Big Changes, Mark Penn (worldwide CEO of Burson-Marsteller and chief adviser to Senator Clinton’s presidential campaign) offers an excellent, concise explanation for exactly why swing voting, as he puts it, is king -

We hear it every day: America is divided into two camps – red and blue – and the key to elections is just energizing the base. Books have been written about it, careers have been made on it, and movements have been founded on it. But it is simply not true …

Just look at the math regarding generating turnout for the base versus courting the swing voters. Voting is based on history – the most likely voters are those who voted last time. Based on that, the case for winning with just the base is daunting. Suppose you have ten voters who voted last time, splitting their preferences 50/50. Now if one swing voter changes his or her mind, the vote becomes 60/40. If one new voter gets added to the pool, thanks to your efforts to turn out the base, the vote is still 55 to 45 against you (you have 6 out of 11). If a second voter who didn’t vote last time is chauffeured to the polls, you are not back to 50/50, as you have 6 out of 12. In other words, it takes two new voters to overcome one voter who has changed his mind, and three new voters to overcome his defection. In almost all cases, therefore, it is more strategic to get one voter on the edge to switch opinions than it is to bring two or three new voters to the polls. It’s theoretically possible for additional base turnout to be a factor, but in 95 perfect of the elections, it is the swing voter who is decisive.

I thought this was worth sharing.

(I’ve included some additional thoughts for discussion in the comments).