Period	Percent
1970-01-01	5.16
1975-01-01	6.00
1980-01-01	6.39
1985-01-01	8.12
1990-01-01	10.86
1995-01-01	14.44
2000-01-01	17.72
2005-01-01	18.00
2010-01-01	15.98