Period	Percent
1970-01-01	21.50
1975-01-01	19.29
1980-01-01	20.70
1985-01-01	23.06
1990-01-01	24.58
1995-01-01	25.96
2000-01-01	24.35
2005-01-01	29.54
2010-01-01	38.00