Year % 1996 22.25 1999 21.05 2000 21.34 2001 18.96 2002 19.13 2003 18.92 2006 13.64 2007 15.57 2010 18.71 2011 19 2012 15.51 2013 15.51 2015 14.86 2016 15.57 2017 15.61 2018 15.72 2019 15.58 2020 15.65 2021 16.85