When an economist says the evidence is "mixed," he or she means that theory says one thing and data says the opposite.

So, what's a nudge? A nudge is some small feature of the environment that attracts our attention and alters our behavior.

Is there a market for somebody selling a credit card that helps people pay down their balances? I think the question is yes. But it would have to be sold by a bank that's really willing to invest in being a trusted partner with its consumers, because they will make less money on each consumer.

Most economists, including me, agree that longevity insurance would make sense for a lot of people.

Rip Van Winkle would be the ideal stock market investor: Rip could invest in the market before his nap and when he woke up 20 years later, he'd be happy. He would have been asleep through all the ups and downs in between. But few investors resemble Mr. Van Winkle. The more often an investor counts his money - or looks at the value of his mutual funds in the newspaper - the lower his risk tolerance.

There are cases when I can make myself better off by restricting my future choices and commit myself to a specific course of action.

I think the people who've been the most overconfident in our business in the last decade have been the people that called themselves risk managers.