A capital idea
My father used to ride to work in a colleague's car. I distinctly remember as a child pressing my nose against the sitting-room window and forlornly watching him standing by the roadside. He did not usually have to wait more than a couple of minutes before he was picked up and driven 15 miles to the big city. Neither of us realised that he was using a mysterious economic asset, "social capital".
Social capital is important but elusive. It is an attempt by social scientists to expand the traditional list of economic assets beyond physical capital, such as computers or roads; and human capital, that is you and me and whatever tricks we've learned along the way. Economists have attempted to account for why, in the words of P.J. O'Rourke, "some parts of the Earth prosper and others suck". But as long as those attempts have simply measured the roads and counted the number of IT graduates, they have failed. Social capital is supposed to explain why, and social scientists, including economists, embraced the concept with enthusiasm.
Francis Fukuyama published Trust, explaining how trusting societies were richer. Robert Putnam offered Making Democracy Work, noting that in southern Italy, it didn't. He then followed up with Bowling Alone, a study of the decline of everything from voting to bowling leagues.
All this is the realm of social capital, but it is a slippery concept. Some kinds of social capital might be rather destructive: the old school-tie network, or patron-client relationships. Social capital will sometimes be a zero-sum game: if I enjoy high status, that is social capital for me, but an improvement in my status will often reduce yours.
Even "good" social capital is hard to measure. One popular way to gauge trust is to ask people whether they think other people can be trusted. Unfortunately, this is a terrible measure of whether people do actually trust each other. Research by economist Ed Glaeser and his colleagues suggested that people who are "trusting" according to the surveys do not actually trust others in simple laboratory experiments. They are, however, more trustworthy. Another popular measure of social capital is the turnout at elections, but it's not at all obvious that voting and social capital are the same thing. It would be much better to measure an activity that cannot happen without social capital.
And so we return to car-pooling. It is not a bad measure of a certain kind of social capital: car-pooling does not work without trust. Can you trust your fellow travellers not to be late, drive badly, or murder you? Whatever it is, social capital would seem to help you get a lift. Economists Kerwin Charles and Patrick Kline have just published a paper about car-pooling and social capital, and there's a twist. Charles and Kline want to understand how the local racial mix affects social capital. They predict that, for instance, African-Americans will find it easier to car-pool if they live in an area with lots of other African-American, following a battery of tedious but handy statistical tests, this is exactly what they find.
They also find that not all racial differences present the same barrier to car-pooling. Asians who are a minority in a chiefly white area car-pool more than Asians who are a minority in a chiefly Afan-American area. African-Americans and Hispanics seem to find it similarly easy to get along. But neither whites in a largely African-American area nor African-Americans in a largely white area tend to car-pool. There is such a thing as social capital, and if you live in an area full of people with the same colour skin as you, it seems you will enjoy more of it.
搭车上班的启示
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我小的时候，父亲曾经搭乘同事的车去上班。我清楚地记得，孩提时代的我把鼻子贴在起居室的窗户上，孤独地看着他站在路边。他一般只需等几分钟就能搭到车，然后共同驱车15英里进城上班。父亲和我都没意识到，当时他正在利用一种神秘的经济资产――“社会资本”。
社会资本很重要，却很难作出精确的界定。它是社会学家在有形资本（如电脑或公路）和人力资本（比如你和我，以及我们在成长过程中学到的所有技能）之外，拓展经济资产传统范畴的一种尝试。经济学家们曾试图解释，为什么“地球上某些地区欣欣向荣，其它地区节节衰败”――P?J?欧鲁克(P.J. O’Rourke)语。但鉴于这些尝试只是简单衡量公路和IT毕业生的数量，所以他们失败了。人们期待社会资本可以作出解释，而社会学家（包括经济学家）殷切接纳了这一概念。
弗朗西斯?福山(Francis Fukuyama)曾出版著作《信任：社会美德与创造经济繁荣》，阐释相互信任的社会为什么会更加富裕。罗伯特?普特南(Robert Putnam)出版了《使民主运转起来》(Making Democracy Work)一书，指出民主在意大利南部并不奏效。他随后出版了《独自玩保龄》(Bowling Alone)，研究从投票选举到保龄球赛一切事物的衰落规律。
所有这些都属于社会资本范畴，但这是一个很难把握的概念。某类社会资本可能更具破坏性：比如校友关系网，或庇护关系(patron-client)。社会资本有时会成为零和游戏(zero-sum game)：如果我位高权重，那是我的社会资本，但我的社会地位的改善，往往会减少你的社会资本。
即使是“好的”社会资本，也很难衡量。衡量信任度的一个流行方法，就是询问人们是否认为他人可信。不幸的是，这是一种糟糕的衡量方法，无法确定人们实际上是否真的彼此信任。
经济学家埃德?格莱泽(Ed Glaeser)及其同事的一项研究表明，通过简单的实验室实验即可发现，在调查中声称“信任别人”的人，实际上并不真正相信他人。不过，他们自己倒是更加值得信任。另一种比较流行的衡量社会资本的方法，是调查参加投票的选民人数比率，但很难说投票选举和社会资本是一回事。更好的方法，是找出一种没有社会资本就不能发生的活动。
因此，让我们回到“搭便车”问题。对某类社会资本而言，这种衡量方式并不坏：“搭便车”离不开信任。你可以信任你的“车友”不会迟到、驾驶技术高超、不会谋杀你吗？无论如何，社会资本似乎可以帮你搭到便车。经济学家克尔温?查尔斯(Kerwin Charles)和帕特里克?克兰(Patrick Kline)刚刚发表了一篇关于搭便车与社会资本的论文，结果证明，二者密切相关。查尔斯和克兰希望了解当地种族混居对社会资本有何影响。例如，他们预测，非洲裔美国人如果居住在非洲裔美国人聚居的地区，会发现“搭便车”要容易一些。经过一系列乏味但有用的统计学调查分析，他们发现结果完全符合预测。
他们还发现，并非所有种族差异都意味着同样的共乘障碍。同样是少数群体，住在白人聚居区的亚洲人就比住在非洲裔美国人聚居区的亚洲人更容易搭到车。同理，非裔美国人和拉美人之间似乎更容易打交道。但无论是白人在非裔美国人聚居区，还是非洲裔美国人在白人聚居区，都不太可能获得“共乘”。这就是社会资本。如果你居住的地区到处都是与你肤色相同的人，你似乎会享受到更多社会资本。
