Year % 1997 15.1 1998 15.5 1999 15.5 2000 15.1 2001 14 2002 13.4 2003 15 2004 15.4 2005 15.2 2006 15.5 2007 15.1 2008 14 2009 13.3 2010 13.2 2011 12.9 2012 12.7 2013 12.5 2014 12 2015 11.6 2016 11.8 2017 11.3 2018 10.8 2019 10.9 2020 9.8