Period	Percent
1970-01-01	4.19
1975-01-01	5.51
1980-01-01	8.30
1985-01-01	10.62
1990-01-01	13.76
1995-01-01	16.55
2000-01-01	20.40
2005-01-01	21.88
2010-01-01	23.61