Period	Percent
1970-01-01	2.25
1975-01-01	0.20
1980-01-01	0.29
1985-01-01	0.55
1990-01-01	0.68
1995-01-01	0.87
2000-01-01	1.46
2005-01-01	1.66
2010-01-01	1.58