Year % 1997 7.524811139090509 1998 8.073674006370313 1999 8.583815028901736 2000 8.428104066053903 2001 9.352409638554215 2002 10.79722939019422 2003 11.088861076345438 2004 11.491809428535705 2005 12.8439219609805 2006 12.839841819080581 2007 14.205844980940281 2008 15.910735826296747 2009 16.785037878787886 2010 16.694175901909926 2011 17.041095890410958 2012 17.638500279798542 2013 18.351920693928133 2014 19.940344675209904 2015 20.19177165793288 2016 20.309437854564212 2017 20.261302364164255 2018 20.084477296726508 2019 20.037966673697543 2020 21.81502764827064 2021 22.27529309596179 2022 23.09944813605136 2023 23.189879137015694