Year Number 1996 22.5 1998 29.8507461547852 2000 28.8557205200195 2002 19.9004974365234 2003 11.9402980804443 2004 10.5769233703613 2005 19.7115383148193 2006 19.7115383148193 2007 16.8269233703613 2008 20.1923084259033 2009 19.9052124023438 2010 15.6398105621338 2011 16.9014091491699 2012 14.5539903640747 2013 7.0422534942627 2014 8.86699485778809 2015 13.7931032180786 2016 19.2118225097656 2017 17.2413787841797 2018 14.5631065368652 2019 14.9758453369141 2020 13.5265703201294 2021 15.4589376449585 2022 15.4589376449585