Period	Percent
1970-01-01	0.29
1975-01-01	0.30
1980-01-01	0.30
1985-01-01	0.73
1990-01-01	1.30
1995-01-01	1.57
2000-01-01	2.20
2005-01-01	2.32
2010-01-01	3.11