Year Number 1996 17.3913040161133 1998 16.8478260040283 2000 19.0217399597168 2002 16.7567558288574 2003 18.3783779144287 2004 12.93532371521 2005 9.80392169952393 2006 14.2156858444214 2007 18.4466018676758 2008 16.990291595459 2009 22.0095691680908 2010 22.4880390167236 2011 23.222749710083 2012 23.222749710083 2013 23.222749710083 2014 28.365385055542 2015 19.5238094329834 2016 17.1428565979004 2017 14.2857141494751 2018 17.1428565979004 2019 16.6666660308838 2020 11.9047622680664 2021 10.4761905670166 2022 15.5660381317139