The figure below shows differing levels of voter confidence in three groups of survey respondents:

1. Pre-election respondents who said they intended to vote
2. Pre-election respondents who said they were uncertain whether they would vote
3. Post-election respondents who reported voting

The most interesting result here, I think, is the substantially lower confidence levels among those who say they are uncertain whether they will vote or not, raising the obvious question whether lower pre-election confidence levels dissuades turnout.

Source: 2008 Cooperative Congressional Election Study