Period	Percent
1970-01-01	3.90
1975-01-01	4.79
1980-01-01	6.80
1985-01-01	7.46
1990-01-01	7.63
1995-01-01	10.82
2000-01-01	13.42
2005-01-01	14.07
2010-01-01	16.30