Year % 1997 15.51945668135096 1998 15.602382043060016 1999 16.80295950155763 2000 17.695937628231434 2001 17.61721319176923 2002 18.22945910537151 2003 18.70299027701339 2004 19.36395115728084 2005 19.76982781693282 2006 20.233220580380987 2007 21.140880056777863 2008 21.34881247784474 2009 21.816570669029684 2010 21.895482728077944 2011 22.424349986689144 2012 22.955005723342428 2013 24.31862141726745 2014 24.71346704871059 2015 25.310350986871494 2016 25.318826362258097 2017 26.737486496218942 2018 27.351034544001422 2019 28.450954283177985 2020 29.403926445767073 2021 30.0194586944985 2022 30.06411993136458 2023 30.25414563806777