Year Number 1996 13.5869569778442 1998 16.8478260040283 2000 16.3043479919434 2002 16.7567558288574 2003 18.9189186096191 2004 20.3980102539063 2005 22.5490188598633 2006 22.5490188598633 2007 25.2427177429199 2008 26.2135925292969 2009 26.3157901763916 2010 26.3157901763916 2011 27.962085723877 2012 26.0663509368896 2013 23.222749710083 2014 17.3076915740967 2015 18.0952377319336 2016 17.1428565979004 2017 16.1904754638672 2018 16.6666660308838 2019 16.6666660308838 2020 14.7619047164917 2021 18.0952377319336 2022 17.9245281219482