Period	Percent
1970-01-01	5.63
1975-01-01	7.44
1980-01-01	10.35
1985-01-01	15.22
1990-01-01	20.87
1995-01-01	28.19
2000-01-01	36.69
2005-01-01	38.15
2010-01-01	39.92