Period	Percent
1970-01-01	3.80
1975-01-01	5.08
1980-01-01	7.20
1985-01-01	9.31
1990-01-01	11.47
1995-01-01	15.45
2000-01-01	20.69
2005-01-01	20.30
2010-01-01	18.08