Who wrote Stumbling on Happiness?

Interview with the author of "Stumbling on Happiness": "Money makes a huge difference to the happiness of poor people. If you live in a cardboard box under a bridge, money can improve your happiness dramatically. But once you have a decent middle-class existence -- food, shelter, security, and all the rest -- money does less and less for you until eventually it does nothing at all. The irony, then, is that in a "rich get richer" society, the people who are getting the money are the people for whom it can do the least, and the people who are not getting the money are the people for whom it could do the most. If a single dollar bill can buy one unit of happiness for a rich person and one hundred units of happiness for a poor person, on whom should that dollar be spent?"