Period	Percent
1970-01-01	2.60
1975-01-01	4.23
1980-01-01	7.00
1985-01-01	9.24
1990-01-01	11.79
1995-01-01	12.61
2000-01-01	13.53
2005-01-01	14.45
2010-01-01	15.92