Period	Percent
1970-01-01	1.40
1975-01-01	1.67
1980-01-01	2.30
1985-01-01	3.91
1990-01-01	6.68
1995-01-01	6.93
2000-01-01	6.91
2005-01-01	6.54
2010-01-01	5.72