| Year | Value | | 2022 | 19.809461964736 | | 2021 | 8.6127675908074 | | 2020 | 11.324356901458 | | 2019 | 19.756626659536 | | 2018 | 21.344520049868 | | 2017 | 19.246149502369 | | 2016 | 17.697498545067 | | 2015 | 14.472189472193 | | 2014 | 15.281721403628 | | 2013 | 15.431986529403 | | 2012 | 14.457226392237 | | 2011 | 10.008044828278 | | 2010 | 10.731500626252 | | 2009 | 0.6570041167702 | | 2008 | 2.9340985018089 | | 2007 | 11.012219098408 | | 2006 | 11.588688507068 | | 2005 | 19.05730828256 | | 2004 | 20.957447928727 | | 2003 | 16.353517131903 | | 2002 | 19.074706779253 | | 2001 | 18.603400566132 | | 2000 | 10.3417460063 | | 1999 | 20.448042353626 | | 1998 | 15.831736080524 | | 1997 | -2.9736558431579 |
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