| Year | Value | | 2022 | 11.602073219927 | | 2021 | 13.400604801181 | | 2020 | 17.721857955799 | | 2019 | 15.721583421577 | | 2018 | 12.031377231097 | | 2017 | 15.786250718833 | | 2016 | 12.494160407609 | | 2015 | 12.360610341869 | | 2014 | 11.607218262965 | | 2013 | 13.740592583426 | | 2012 | 14.231733905397 | | 2011 | 18.484389189911 | | 2010 | 24.129971622998 | | 2009 | 11.553458696335 | | 2008 | 10.653801655525 | | 2007 | 8.2942480327734 | | 2006 | 13.239462816219 | | 2005 | 9.9150132136141 | | 2004 | 10.583428938646 | | 2003 | 15.818207942959 | | 2002 | 9.049277792502 | | 2001 | 6.21281626432 | | 2000 | 6.9034366807001 | | 1999 | 26.572812435346 | | 1998 | 25.788831075289 | | 1997 | 23.182984381365 | | 1996 | 26.915983585609 | | 1995 | 26.434058686438 | | 1994 | 0.96854490633186 | | 1993 | -4.556622916597 | | 1992 | 11.0654587038 | | 1991 | 11.407535726842 | | 1990 | 2.9678100544723 | | 1989 | 9.732087089608 | | 1988 | 7.82784212626 |
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