Year % 1997 31.52 1999 33.25 2000 18.21 2001 17.47 2002 15.24 2003 13.85 2004 13.75 2005 13.81 2006 11.57 2007 11.64 2008 11.06 2009 11.09 2010 11.94 2012 12.11 2013 12.15 2018 16.98 2019 19.36 2020 10.83 2021 10.41