| Year | Value | | 2021 | 16.908849519203 | | 2020 | 14.145787232581 | | 2019 | 16.850520916519 | | 2018 | 16.688528314198 | | 2017 | 13.546908446892 | | 2016 | 11.350993451542 | | 2015 | 11.894137923062 | | 2014 | 12.901634244679 | | 2013 | 15.731208036979 | | 2012 | 15.312142183817 | | 2011 | 18.466991091551 | | 2010 | 19.593119250577 | | 2009 | 16.540294403425 | | 2008 | 21.65181536039 | | 2007 | 23.479176478542 | | 2006 | 28.709974678687 | | 2003 | 18.038745571348 | | 2002 | 13.369240222564 | | 2001 | 14.662059187239 | | 2000 | 13.910160696328 | | 1999 | 9.8058178776212 | | 1998 | 8.3586720873341 | | 1997 | 10.572433151476 | | 1996 | 9.6023478161415 | | 1995 | 9.7739563560805 | | 1994 | 11.324164929469 | | 1993 | 17.517329020918 | | 1992 | 11.081365740344 |
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