Period	Percent
1970-01-01	2.35
1975-01-01	3.62
1980-01-01	5.30
1985-01-01	6.57
1990-01-01	7.77
1995-01-01	10.07
2000-01-01	12.02
2005-01-01	14.91
2010-01-01	17.67