Year % 1997 9.09090909090909 1998 9.09090909090909 1999 9.09090909090909 2000 9.09090909090909 2002 2 2003 2 2004 2 2005 14.7826086956522 2006 15.0724637681159 2008 6.33333333333333 2009 18.5507246376812 2010 18.5507246376812 2011 19.7142857142857 2012 19.7142857142857 2013 19.7142857142857 2014 19.8275862068966 2015 20 2016 20 2017 20.2857142857143 2018 20.2857142857143 2019 20.6303724928367 2020 20.9169054441261 2021 20.8571428571429 2022 20.8571428571429 2023 20.8571428571429