When partisans are asked to do just that, they become less partisan:
Without any money involved, Democrats’ estimates of the change in unemployment under Bush were about 0.9 points higher than Republicans’ estimates. But when correct answers were rewarded, that gap shrank to 0.4 points. When correct answers and “don’t knows” were rewarded, it shrank to 0.2 points. [Political scientists John Bullock, Alan Gerber, Gregory Huber and Seth Hill] conclude that false answers — like Democrats saying that casualties in Iraq increased from 2007 to 2008 — are just cheap talk, a way to signal a party affiliation rather than a sincere belief.
The Dish 