Year Percent 1980-01-01 0.49644499999999997 1981-01-01 0.48623100000000000 1982-01-01 0.42167400000000000 1983-01-01 0.35469400000000000 1984-01-01 0.54218000000000000 1985-01-01 0.64013800000000000 1986-01-01 0.56677300000000000 1987-01-01 0.49540600000000000 1988-01-01 0.49540600000000000 1989-01-01 0.49540600000000000 1990-01-01 0.49540600000000000 1991-01-01 0.49540600000000000 1992-01-01 0.49540600000000000 1993-01-01 0.49540600000000000 1994-01-01 0.49540600000000000 1995-01-01 0.49540600000000000 1996-01-01 0.49540600000000000 1997-01-01 2.38023000000000000 1998-01-01 5.14779000000000050 1999-01-01 5.08785000000000000 2000-01-01 9.76435000000000000 2001-01-01 18.05360000000000000 2002-01-01 18.74550000000000000 2003-01-01 17.02690000000000000 2004-01-01 21.93520000000000000 2005-01-01 22.03750000000000000 2006-01-01 24.07610000000000000 2007-01-01 22.73540000000000000 2008-01-01 24.28530000000000000 2009-01-01 25.27370000000000000 2010-01-01 23.08590000000000000 2011-01-01 21.33740000000000000 2012-01-01 18.94580000000000000 2013-01-01 19.68430000000000000 2014-01-01 24.75200000000000000 2015-01-01 35.75790000000000000 2016-01-01 41.82270000000000000