Period	Percent
1970-01-01	8.01
1975-01-01	9.53
1980-01-01	10.90
1985-01-01	12.21
1990-01-01	13.40
1995-01-01	14.21
2000-01-01	14.41
2005-01-01	15.76
2010-01-01	17.98