Year % 2000 18.5 2001 18.5 2002 17.6 2003 17.7 2004 16.7 2005 16.1 2006 15.6 2007 15.1 2008 14.2 2009 14.2 2010 13.5 2011 13.3 2012 13.1 2013 13 2014 12.4 2015 12.8 2016 12.1 2017 12.3 2018 12.1 2019 11.4