Unexpectedly Intriguing!
November 18, 2008

What is the probability that Senator Norm Coleman is really leading Al Franken in the polls for the U.S. Senate seat now being contested in Minnesota?

To answer that question, we've adapted our tool for finding the odds that a given candidate's lead in the polls reflects what the final outcome of an election will be. That tool reworked the math presented by Supercrunchers' author Ian Ayres in an Excel spreadsheet that, in our view, wasn't the easiest thing in the world to figure out how to use. We did an extreme makeover of Ian's user interface, developing it into a much more user-friendly format!

Today, we're going to rework that tool again to answer our question! First though, let's see where the current vote counts stand:

Minnesota U.S. Senator Vote Tallies, 15 November 2008
Norm Coleman 1,211,565 1,708,853
Al Franken 1,211,359 1,709,059
All Others 462,578 2,457,840
All Candidates 2,885,502 34,916

Taking the vote tally as of 15 November 2008 as kind of "superpoll," what we're really trying to find is the odds that Norm Coleman will retain his lead after all the ballots ruled valid in the original election count have been recounted.

What makes that less than a sure thing is the possibility of machine error in originally counting the ballots. Here, assuming that all the ballots originally counted for each candidate are valid, we need to take into account the number of ballots for which no vote for any U.S. Senate candidate was recorded, since this provides the pool of votes from which the final vote tallies produced in a recount may be drawn, provided that they contain a clear indication favoring a given candidate. Nate Silver indicates that the number of non-disqualified ballots is 34,916.

Combined with the number of ballots counted for all candidates, 2,885,502, this sum tells us the size of the total population of qualified ballots: 2,920,418. We'll take this total, as well as official vote tallies for both Norm Coleman and Al Franken and use our tool to find the likelihood that Senator Coleman will retain his lead, which has been certified by the state election board of Minnesota:

Polling Data
Input Data Values
How many ballots have not been rejected?
How many ballots have been cast favoring the candidate who appears to be leading?
How many ballots cast favor the other main candidate in the race?

Who's Really Out in Front?
Calculated Results Values
Probability that the Candidate Who Appears to Be Leading, Actually Is Leading

Using the tool with the vote totals recorded as of 15 November 2008, we find that the probability that Senator Coleman will retain his lead to be 55.8%. We do note that an additional nine votes have been counted in Senator Coleman's favor following an audit of Minnesota's voting machines, which have not been added to his vote total entered in the tool above - you're welcome to modify the values in the tool above to reflect these votes or other potential uncounted vote scenarios!

We find that 55.8% to be a fairly narrow, but positive margin, which perhaps explains why Al Franken has launched a number of lawsuits in an as-yet failing attempt to pad the total ballot count in order to maximize his chances of winning the recount.

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