Period	Percent
1970-01-01	3.70
1975-01-01	2.54
1980-01-01	1.37
1985-01-01	2.30
1990-01-01	5.27
1995-01-01	9.29
2000-01-01	8.89
2005-01-01	7.62
2010-01-01	6.14