Period	Percent
1970-01-01	7.43
1975-01-01	12.30
1980-01-01	14.43
1985-01-01	16.36
1990-01-01	18.86
1995-01-01	21.59
2000-01-01	23.16
2005-01-01	27.02
2010-01-01	28.15