Period	Percent
1970-01-01	4.10
1975-01-01	4.81
1980-01-01	6.00
1985-01-01	7.41
1990-01-01	9.53
1995-01-01	11.21
2000-01-01	11.66
2005-01-01	13.75
2010-01-01	17.28