Year % 1997 12.26 1998 8.26 1999 8.32 2000 8.17 2001 7.97 2002 8.26 2003 7.83 2004 7.82 2005 7.41 2006 7.67 2007 7.4 2008 7.31 2009 7.76 2010 7.48 2011 7.3 2012 7.28 2013 6.93 2015 7.37 2020 6.19 2021 5.99