The amount of community spirit or trust that an economy has gluing it together. The more social capital there is, the more productive the economy will be. Yet, curiously, one of the best-known books to address the role of social capital, "Bowling Alone", by Robert Putnam of Harvard University, pointed out that Americans were far less likely to be members of community organizations, clubs or associations in the 1990s than they were in the 1950s. He illustrated his thesis by charting the decline of bowling leagues. Yet the American economy has gone from strength to strength. This has led some economists to question whether social capital is really as important as the theory suggests, and others to argue that membership of bowling leagues and other community organizations is simply not a good indicator of the amount of social capital in a country.