Year % 1998 16.046831955922887 1999 16.84560713745655 2000 16.357597564350957 2001 16.55372700871249 2002 17.216758722888326 2003 16.06960081883318 2004 16.625342555135088 2005 16.90890215416558 2006 17.28579175704989 2007 17.750230779374903 2008 17.95848660010509 2009 18.333987184516804 2010 17.769423558897238 2011 17.698677542948946 2012 17.856703944942847 2013 18.82742548755061 2014 18.595512739257206 2015 19.28737412858251 2016 19.42618806875634 2017 19.810606060606045 2018 20.235707121364097 2019 20.503814944895232 2020 21.33004926108374 2021 21.38448505385453 2022 21.927587965323813 2023 22.527332824815673