Period	Percent
1970-01-01	2.00
1975-01-01	2.08
1980-01-01	2.28
1985-01-01	2.51
1990-01-01	2.78
1995-01-01	2.68
2000-01-01	2.80
2005-01-01	2.54
2010-01-01	2.17