Period	Percent
1970-01-01	5.10
1975-01-01	5.89
1980-01-01	7.00
1985-01-01	8.57
1990-01-01	10.11
1995-01-01	10.96
2000-01-01	12.64
2005-01-01	15.12
2010-01-01	19.43