Period	Percent
1970-01-01	4.10
1975-01-01	4.62
1980-01-01	6.00
1985-01-01	9.28
1990-01-01	13.70
1995-01-01	12.26
2000-01-01	11.77
2005-01-01	12.47
2010-01-01	16.52