Year % 1997 11.0599078341014 1998 12.4423963133641 1999 12.4423963133641 2000 11.2612612612613 2001 17.7570093457944 2002 17.7570093457944 2003 17.7570093457944 2004 15.2542372881356 2005 15.2542372881356 2006 15.2542372881356 2007 20.5020920502092 2008 20.5020920502092 2009 20.9737827715356 2010 22.1428571428571 2011 22.887323943662 2012 22.887323943662 2013 27.3356401384083 2014 27.3356401384083 2015 27.2413793103448 2016 29.7945205479452 2017 29.4520547945205 2018 29.4520547945205 2019 27.9605263157895 2020 27.9605263157895 2021 27.9605263157895 2022 27.3311897106109 2023 27.3311897106109