| Year | Value | | 2021 | 9.4471113630955 | | 2020 | 8.3188093138288 | | 2019 | 11.78694274063 | | 2018 | 11.717799586588 | | 2017 | 10.303011375612 | | 2016 | 9.92425019653 | | 2015 | 9.8357115521941 | | 2014 | 14.193432739719 | | 2013 | 16.030177764619 | | 2012 | 13.312098150159 | | 2011 | 18.257834210065 | | 2010 | 15.71238046365 | | 2004 | 13.908677966703 | | 2003 | 13.083237653072 | | 2002 | 12.134359783377 | | 2001 | 9.6423006532377 | | 2000 | 10.22139507126 | | 1999 | 7.7453699343745 | | 1998 | 7.2947938960233 | | 1997 | 6.7872205867622 |
|