Year % 1984 27 1987 26.1 1990 27 1993 27.8 1996 29.7 1998 26.8 1999 27.3 2000 25 2001 25.6 2002 27.7 2003 27.2 2004 27.7 2005 28 2006 28.8 2007 29.6 2008 29.1 2009 29.4 2010 29.5 2011 32.6 2012 32.9 2013 32.9 2014 32.5 2015 33 2016 31 2017 30.2 2018 29.9 2019 29.5 2020 29.5 2021 30.1 2022 30.7 2023 31.4