Period	Percent
1970-01-01	4.60
1975-01-01	6.06
1980-01-01	7.81
1985-01-01	11.79
1990-01-01	14.60
1995-01-01	19.06
2000-01-01	25.17
2005-01-01	31.77
2010-01-01	44.25