Period	Percent
1970-01-01	0.15
1975-01-01	0.25
1980-01-01	0.35
1985-01-01	0.49
1990-01-01	0.58
1995-01-01	0.56
2000-01-01	0.56
2005-01-01	0.59
2010-01-01	0.87