Year % 1997 3.747161241483725 1998 3.457446808510639 1999 3.6167756829549806 2000 3.77068103116583 2001 4.621264767199441 2002 6.130931763075857 2003 6.048109965635739 2004 6.69304319155952 2005 7.036766496225965 2006 9.34959349593497 2007 9.753765240258197 2008 9.801577814965343 2009 9.902309058614565 2010 11.919671777153956 2011 11.328502415458932 2012 14.872042491549967 2013 17.36930860033727 2014 17.7934018388318 2015 18.77984084880636 2016 19.27561399156537 2017 18.884021212819935 2018 19.060773480663 2019 17.56653992395439 2020 19.546958513616715 2021 18.22454308093995 2022 18.24625886059333 2023 17.728237791932056