| Year | Value | | 2021 | 27.009985064378 | | 2020 | 29.561587256443 | | 2019 | 19.083352699443 | | 2018 | 19.804639337392 | | 2017 | 22.054890579249 | | 2016 | 24.704440494765 | | 2015 | 18.015372126872 | | 2014 | 18.896620025919 | | 2013 | 19.069182514987 | | 2012 | 23.838637666394 | | 2011 | 9.3493442741976 | | 2010 | 8.8531645500443 | | 2009 | 12.854380037904 | | 2008 | 10.901931453961 | | 2007 | 11.000556050041 | | 2006 | 12.293086262398 | | 2005 | 13.475680538196 | | 2004 | 14.596237995113 | | 2003 | 14.756872496201 | | 2002 | 12.763204169785 | | 2001 | 12.707018592201 | | 2000 | 13.142023772973 | | 1999 | 16.695978991495 | | 1998 | 19.104554584442 | | 1997 | 18.762630515325 | | 1996 | 19.553312903697 | | 1995 | 20.553723121568 | | 1994 | 22.730518925335 | | 1993 | 23.621009693609 | | 1992 | 27.266774062578 | | 1991 | 27.314875948178 | | 1990 | 27.435218769402 |
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