Period	Percent
1970-01-01	6.10
1975-01-01	9.64
1980-01-01	11.72
1985-01-01	13.78
1990-01-01	13.79
1995-01-01	20.23
2000-01-01	26.87
2005-01-01	30.04
2010-01-01	31.61