Period	Percent
1970-01-01	14.80
1975-01-01	17.99
1980-01-01	23.10
1985-01-01	25.47
1990-01-01	28.59
1995-01-01	32.10
2000-01-01	36.53
2005-01-01	41.07
2010-01-01	43.25