Period	Percent
1970-01-01	5.40
1975-01-01	5.46
1980-01-01	5.70
1985-01-01	6.44
1990-01-01	6.97
1995-01-01	9.43
2000-01-01	12.77
2005-01-01	15.28
2010-01-01	21.13