As can be seen on the chart there is a strong correlation between GDP per Capita and Median Family Income. For the first three decades after WWII the two were perfectly correlated. After 1975 both continued to grow, however GDP per capita has been growing faster than Median Family Income.

This chart is from The Size and Functions of Government and Economic Growth study performed for for the Congressional Joint Economic Committee.  The chart summarizes the regression analysis performed that shows a negative relationship between the size of government and economic growth. The study included data from over a 36 year period for all industrialized countries. The study also revealed that after 20%, most of the increase in the size of government is due to transfer payments (i.e. welfare programs, corporate subsidies, etc.).