可以肯定的是，世上有两种幸福：一种是侧重于日常心情的幸福，另一种则是在世上安身立命的广义幸福，普林斯顿大学（Princeton University）经济学家安格斯•迪顿和著名的心理学家丹尼尔•卡纳曼将后者称为“人生评估”。迪顿和卡纳曼在2010年的一项研究中发现，随着收入的提高，人们的日常幸福感相应增加。不过一旦年收入达到7万5千美元，幸福感却不再上升了。当然，这个临界值放在纽约市这样的地方就不那么准确了。但《纽约时报》（New York Times）最近也提出，由于纽约的收入差别很大，中产阶级是个含糊的概念。
这种说法很有道理。财富虽然不能买到所有的幸福，但它是提高生活水平的重要途径。根据经济合作与发展组织（Organisation for Economic Co-operation and Development，简称：OECD）的统计，美国人的平均年收入是37,708美元，远高于这个组织34个发达成员国人均22,387美元的年收入。
总体来看，美国在OECD更美好生活指数（Better Life Index）中的排名相当高。这个指数根据国民享受的教育和医疗等情况来衡量一国居民的幸福感。虽然美国人总体上是幸福的，但就算金钱确实能买来幸福，仍然有不少美国人不幸福。美国贫富差距相当大：最富有的20%的美国人收入是底层20%人的8倍。
To be sure, there are two kinds of happinesses: The day-to-day kind that focuses on your daily mood vs. what Princeton University economist Angus Deaton and famed psychologist Daniel Kahneman call "life assessment," which means broader satisfaction with your place in the world. In their 2010 study, they found that day-to-day happiness rises as people earn more money, but once they hit $75,000 a year, they don't get any happier. Admittedly that threshold seems arbitrary in places like New York City, where, as The New York Times recently highlighted, middle-class is a vague class, since incomes there vary so widely.
Nonetheless, according to Deaton and Kahneman, the more money people have, the more likely they'll feel they have a better life. This taps into the keeping up with the Joneses mindset: If I earn more, I could buy a fancier car than Mr. Jones next door. Or if I earn more, I may be able to donate more of my fortune than Warren Buffett or some other rich person.
Wolfers's and Stevenson's study speaks to the latter kind of happiness, where fulfillment is infinite so long as your income rises.
This makes a lot of sense. Money, while it can't always buy happiness, is an important means to achieving higher living standards. In the U.S., the average person earns $37,708 a year, according to the Organisation for Economic Co-Operation and Development. That's more than the average of $22,387 of the OECD's 34-member developed countries.
Overall, the U.S. ranks pretty high in the OECD's Better Life Index, which measures the happiness of countries based on, among other things, access to education and health care. Though Americans are generally happy, there are still a lot of unhappy folks if money does indeed buy happiness. There's a considerable gap between the richest and poorest -- the top 20% of the population earn about eight times as much as the bottom 20%.
So if happiness is what you want, look inward, rather than what your neighbors might have. Sounds obvious, but sometimes it takes a team of economists to prove it.