Period	Percent
1970-01-01	3.10
1975-01-01	5.50
1980-01-01	6.90
1985-01-01	7.70
1990-01-01	13.05
1995-01-01	16.55
2000-01-01	19.74
2005-01-01	20.49
2010-01-01	24.27