Period	Percent
1970-01-01	2.27
1975-01-01	5.05
1980-01-01	7.10
1985-01-01	7.84
1990-01-01	8.38
1995-01-01	12.35
2000-01-01	18.94
2005-01-01	23.63
2010-01-01	25.67