Period	Percent
1970-01-01	2.00
1975-01-01	2.29
1980-01-01	3.40
1985-01-01	5.24
1990-01-01	7.47
1995-01-01	7.62
2000-01-01	7.51
2005-01-01	3.74
2010-01-01	10.42