Democratic voters tend to be more likely to be first time voters, lower income and younger. As a result they make more mistakes on ballots that are uncovered in hand recounts.
http://www.fivethirtyeight.com/2008/11/frankens-odds-of-winning-recount-may-be.htmlUntil now, however, we have been assuming that ballot tabulation errors are equally likely to favor Franken and Coleman -- but this is probably not the case. Why not? There is substantial evidence that undervotes and overvotes are significantly more common among what we might call vulnerable voters -- in particular, minorities, elderly voters, low-income and low-education voters, and first-time voters. A 2001 study for the House Committee on Government Reform, found that undervoted ballots were more than twice as common in minority-heavy, low-income precincts than in predominately white, upper-income precincts -- even when using the relatively reliable, precinct-based optical scanning system that Minnesota uses. (The discrepancies are significantly higher when using less reliable technologies like punch cards.)
Among other groups of vulnerable voters, however, Franken sigificantly outperformed Coleman. Franken led by 15 points among voters making $50,000 or less, while Coleman led by 3 among voters making between $50,000 and $100,000, and by 16 among voters making $100,000 or more. Coleman won white voters by 3 points, but Franken won among minorities by 40 points. And while there is no direct evidence of this in the exit polls, it is likely that Franken performed significantly better than Coleman among first-time voters.
Assume that minorities are 50% more likely than white voters to have undervoted the ballot; this is arguably a conservative assumption. If this is the case, than about 51.0% of reclassified ballots (excluding those cast for third parties) are likely to be resolved in Franken's favor. Alternatively, suppose that voters making $50,000 or less are 50% more likely than wealthier voters to have undervoted the ballot. In this case, 51.3% of reclassified ballots would go to Franken. This might not seem like a big deal, but as you'll see in a moment, it makes a huge amount of difference.
If, over the long run, we expect Franken to win 51% of corrected ballots, his odds of winning the recount may be quite strong -- in fact, he may be the prohibitive favorite depending on the number of recounted ballots: