Year Number 1996 13.5 1998 13.4328355789185 2000 8.95522403717041 2002 10.945273399353 2003 9.95024871826172 2004 10.0961542129517 2005 13.4615383148193 2006 20.6730766296387 2007 14.4230766296387 2008 11.5384616851807 2009 13.2701425552368 2010 13.7440757751465 2011 23.0046939849854 2012 24.8826293945313 2013 26.7605628967285 2014 27.5862064361572 2015 28.5714282989502 2016 28.5714282989502 2017 28.5714282989502 2018 30.5825233459473 2019 28.019323348999 2020 26.0869560241699 2021 25.6038646697998 2022 22.7053146362305