Period	Percent
1970-01-01	21.30
1975-01-01	27.10
1980-01-01	30.00
1985-01-01	38.84
1990-01-01	45.36
1995-01-01	46.54
2000-01-01	52.01
2005-01-01	53.05
2010-01-01	57.28