Period	Percent
1970-01-01	9.60
1975-01-01	11.90
1980-01-01	15.20
1985-01-01	17.94
1990-01-01	18.70
1995-01-01	21.92
2000-01-01	25.69
2005-01-01	25.12
2010-01-01	24.22