Period	Percent
1970-01-01	0.20
1975-01-01	0.34
1980-01-01	0.45
1985-01-01	0.59
1990-01-01	0.71
1995-01-01	0.81
2000-01-01	0.93
2005-01-01	0.84
2010-01-01	0.80