Year Number 1996 14.5 1998 18.4079608917236 2000 12.93532371521 2002 13.4328355789185 2003 20.8955230712891 2004 18.269229888916 2005 22.115385055542 2006 19.230770111084 2007 19.230770111084 2008 15.865385055542 2009 15.1658763885498 2010 13.7440757751465 2011 14.0845069885254 2012 15.4929580688477 2013 17.8403759002686 2014 21.674877166748 2015 22.660099029541 2016 22.660099029541 2017 22.660099029541 2018 21.8446598052979 2019 22.2222213745117 2020 23.1884059906006 2021 28.5024147033691 2022 28.019323348999