Period	Percent
1970-01-01	6.79
1975-01-01	8.74
1980-01-01	11.33
1985-01-01	13.82
1990-01-01	15.00
1995-01-01	15.82
2000-01-01	18.38
2005-01-01	19.88
2010-01-01	23.53