Period	Percent
1970-01-01	3.95
1975-01-01	4.89
1980-01-01	7.05
1985-01-01	8.15
1990-01-01	10.60
1995-01-01	12.05
2000-01-01	15.20
2005-01-01	17.22
2010-01-01	22.30