Period	Percent
1970-01-01	0.29
1975-01-01	0.30
1980-01-01	0.34
1985-01-01	0.37
1990-01-01	0.60
1995-01-01	0.72
2000-01-01	0.84
2005-01-01	1.04
2010-01-01	1.31