Talking to women about birth can be polarizing.

Every time you have a carrot instead of a cookie, every time you go to the gym instead of going to the movies, that's a costly investment in your health. But how much you want to invest is going to depend on how much longer you expect to live in the future, even if you don't make those investments.

Even if you are planning a birth with an epidural, the evidence suggests that a doula can help make things go much more smoothly.

I've always loved doing research. I remember doing a research project on the Babylonian numeral system in the eighth grade and thinking, 'This is pretty awesome - is this really a job you can have?' This led me toward a career as an academic, although it took me until college to realise that economics was the right field.

I think, always, with a new book, I get nervous. I think mostly it is because work is really important to me, and a book doing well is important because it buys you another one. Not because of the money but if you keep doing interesting work, work that people like, they will want you to do more, and offers that are interesting come in.

I'm not a money manager, but I can tell you what the conventional wisdom is. The younger you are, the more risk you can take on.

Shark Tank' has been a sincere joy. As our traditional venture-backed companies get bigger, the investing side tends to get more political and complicated. 'Shark Tank' takes me back to my early days working with ambitious founders in their earliest and scrappiest days. The show reminds me of what I deeply love about this business.

The middle class is a group defined by more than just money: it also leans on credentials, education, aspirations, assets, and, of course, household income.