Between 1900 and 2000, real gross domestic product per capita (the output of goods and services per person) grew more than 600 percent. Meanwhile, net business investment declined 70 percent as a share of G.D.P. What’s more, in 1900 almost all investment came from the private sector — from companies, not from government — whereas in 2000, most investment was either from government spending (out of tax revenues) or “residential investment,” which means consumer spending on housing, rather than business expenditure on plants, equipment and labor.