Period	Percent
1970-01-01	0.30
1975-01-01	0.58
1980-01-01	1.10
1985-01-01	2.36
1990-01-01	4.18
1995-01-01	3.79
2000-01-01	3.73
2005-01-01	3.60
2010-01-01	3.35