Period	Percent
1970-01-01	4.53
1975-01-01	6.68
1980-01-01	8.50
1985-01-01	9.37
1990-01-01	11.44
1995-01-01	13.79
2000-01-01	17.05
2005-01-01	19.81
2010-01-01	24.43