Period	Percent
1970-01-01	3.52
1975-01-01	5.39
1980-01-01	7.60
1985-01-01	9.03
1990-01-01	10.61
1995-01-01	13.36
2000-01-01	15.34
2005-01-01	23.27
2010-01-01	26.84