Period	Percent
1970-01-01	2.59
1975-01-01	3.62
1980-01-01	4.72
1985-01-01	5.51
1990-01-01	6.08
1995-01-01	6.10
2000-01-01	7.43
2005-01-01	4.50
2010-01-01	1.46