Period	Percent
1970-01-01	2.16
1975-01-01	2.80
1980-01-01	3.27
1985-01-01	4.24
1990-01-01	4.90
1995-01-01	3.29
2000-01-01	1.54
2005-01-01	1.30
2010-01-01	1.08