Year Number 1996 20.5 1998 24.3781089782715 2000 15.9203977584839 2002 18.4079608917236 2003 12.93532371521 2004 16.3461532592773 2005 13.4615383148193 2006 18.75 2007 15.865385055542 2008 16.3461532592773 2009 16.5876770019531 2010 14.6919431686401 2011 15.962441444397 2012 16.4319248199463 2013 15.962441444397 2014 19.2118225097656 2015 16.2561569213867 2016 14.2857141494751 2017 14.2857141494751 2018 16.5048542022705 2019 17.3913040161133 2020 17.3913040161133 2021 19.8067626953125 2022 21.2560386657715