Year % 1984 33.5 1987 31.4 1990 32.3 1993 33.2 1996 35.6 1998 32.2 1999 32.1 2000 29.5 2001 30 2002 32.8 2003 33 2004 33.9 2005 34.1 2006 35.3 2007 36.7 2008 36.1 2009 36 2010 37.2 2011 40.5 2012 40.5 2013 40.8 2014 40.2 2015 40.4 2016 39.3 2017 38.8 2018 38.4 2019 37.6 2020 37.6 2021 37.9 2022 37.9 2023 38.3