Year	Percent
1968-01-01	5.00
1969-01-01	5.00
1970-01-01	5.00
1971-01-01	6.00
1972-01-01	6.00
1973-01-01	7.00
1974-01-01	9.00
1975-01-01	9.00
1976-01-01	9.00
1977-01-01	9.00
1978-01-01	9.00
1979-01-01	9.00
1980-01-01	9.00
1981-01-01	10.00
1982-01-01	10.00
1983-01-01	10.00
1984-01-01	10.00
1985-01-01	10.00
1986-01-01	10.00
1987-01-01	10.00
1988-01-01	10.00
1989-01-01	10.00
1990-01-01	10.00
1991-01-01	12.00
1992-01-01	12.00
1993-01-01	12.00
1994-01-01	12.00
1995-01-01	12.00
1996-01-01	12.00
1997-01-01	9.00
1998-01-01	9.00
1999-01-01	8.00
2000-01-01	8.00
2001-01-01	6.50
2002-01-01	6.25
2003-01-01	6.00
2004-01-01	6.00
2005-01-01	6.00
2006-01-01	6.00
2007-01-01	6.00
2008-01-01	6.00
2009-01-01	6.00
2010-01-01	6.00
2011-01-01	6.00
2012-01-01	9.00
2013-01-01	8.75
2014-01-01	9.00
2015-01-01	7.75
2016-01-01	6.75
2017-01-01	6.25