Period	Percent
1970-01-01	3.08
1975-01-01	3.80
1980-01-01	7.10
1985-01-01	7.70
1990-01-01	10.60
1995-01-01	12.30
2000-01-01	14.60
2005-01-01	21.60
2010-01-01	17.21