@techreport{NBERw9041,
 title = "Relational Costs and the Production of Social Capital: Evidence from Carpooling",
 author = "Kerwin Charles and Patrick Kline",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Working Paper Series",
 number = "9041",
 year = "2002",
 month = "July",
 URL = "http://www.nber.org/papers/w9041",
}