I'm a big fan of asking people to specify their confidence level rather than simply asking if they're confident or not.
An obvious way to do this is ask for a 1-10 rating. Good start.
To quickly increase the quality of discussion, add this wrinkle: **1-10, no 7s**.
Why?
• 7 is the fence.
• 7 is the most common number people will pick when asked.
• 7 is safe.
Make people choose: is it more like a 6, or more like an 8?
Force people off the fence. Real discussions will follow.