"It is difficult to get a man to understand something, when his salary depends upon his not understanding it!"
Bullock, et al., 2013:
In both experiments, all subjects were asked factual questions, but some were given financial incentives to answer correctly. In both experiments, we find that the incentives reduce partisan divergence substantially–on average, by about 55% and 60% across all of the questions for which partisan gaps appear when subjects are not incentivized. But offering an incentive for accurate responses will not deter cheerleading among those who are unsure of the correct factual response, because such people stand to gain little by forgoing it. In our second experiment, we therefore implement a treatment in which subjects were offered incentives both for correct responses and for admitting that they did not know the correct response. We find that partisan gaps are even smaller in this condition–about 80% smaller than for unincentivized responses. This finding suggests that partisan divergence is driven by both expressive behavior and by respondents’ knowledge that they do not actually know the correct answers.
(h/t Bryan Caplan http://econlog.econlib.org/archives/2013/06/the_myth_of_the_8.html)