Period	Percent
1970-01-01	3.34
1975-01-01	4.48
1980-01-01	5.34
1985-01-01	5.40
1990-01-01	6.17
1995-01-01	7.08
2000-01-01	8.25
2005-01-01	10.47
2010-01-01	13.49