Period	Percent
1970-01-01	2.23
1975-01-01	3.20
1980-01-01	7.60
1985-01-01	9.59
1990-01-01	12.68
1995-01-01	13.99
2000-01-01	14.94
2005-01-01	13.36
2010-01-01	11.55