Year % 1997 11.828240252897793 1998 12.784909614880805 1999 12.515151515151517 2000 14.800360252176528 2001 15.426997245179063 2002 16.657824933687 2003 16.674733785091966 2004 17.38329238329239 2005 19.305943358595933 2006 19.772545889864325 2007 20.22630834512023 2008 21.444201312910288 2009 22.38086050549874 2010 22.642244738893215 2011 25.246212121212128 2012 25.02227766886473 2013 25.91505524861879 2014 25.746907706945773 2015 28.149710068529256 2016 28.98916967509025 2017 28.70592262923658 2018 28.771570134973526 2019 29.274563820018376 2020 30.128447298828885 2021 30.47478836952523 2022 30.523627075351218 2023 30.518059102517334