Year % 1992 22.9 1993 23.2 1995 30.4 1996 27.6 2002 23.2 2003 23.3 2004 23.1 2005 23.2 2006 24.1 2007 22 2008 21.9 2009 21.2 2010 21 2011 20.7 2012 20.8 2013 21.1 2014 20.6 2015 21.6 2016 21.2 2017 21.7 2018 22 2019 22.3 2020 21.8