Year Percent 1980-01-01 8.31250 1981-01-01 8.25000 1982-01-01 8.25000 1983-01-01 7.00000 1984-01-01 7.25000 1985-01-01 7.25000 1986-01-01 7.41667 1987-01-01 8.25000 1988-01-01 8.33333 1989-01-01 8.70833 1990-01-01 9.00000 1991-01-01 9.00000 1992-01-01 9.00000 1993-01-01 9.00000 1994-01-01 9.00000 1995-01-01 9.00000 1996-01-01 9.00000 1997-01-01 9.00000 1998-01-01 9.00000 1999-01-01 9.00000 2000-01-01 9.00000 2001-01-01 9.00000 2002-01-01 9.00000 2003-01-01 9.00000 2004-01-01 9.00000 2005-01-01 3.18667 2006-01-01 7.39000 2007-01-01 5.73000 2008-01-01 5.23000 2009-01-01 6.58000 2010-01-01 4.42000 2011-01-01 5.60000 2012-01-01 6.16000 2013-01-01 3.14000 2014-01-01 4.38000 2015-01-01 2.93000