| Year | Value | | 2019 | 4.2574620433543 | | 2018 | 3.6260414135296 | | 2017 | -1.0282817876201 | | 2016 | 0.93119598707956 | | 2015 | 0.47476359734264 | | 2014 | 0.42144091888121 | | 2013 | -2.3720652425226 | | 2012 | 0.62747199289337 | | 2011 | 4.316297421952 | | 2010 | 2.0781407186079 | | 2009 | -2.1354287204694 | | 2008 | 8.9559870517778 | | 2007 | 5.3925678447552 | | 2006 | 3.6080243878454 | | 2005 | 3.3977867782881 | | 2004 | 2.5291294693276 | | 2003 | 3.6563650793842 | | 2002 | 3.3152467858542 | | 2001 | 2.8836043031626 | | 2000 | 4.0440213119051 | | 1999 | 2.2803719825875 | | 1998 | 1.8694885361554 | | 1997 | 2.9999480977841 | | 1996 | 3.2252879721398 | | 1995 | 3.361391073209 | | 1994 | 6.3110797127044 | | 1993 | 5.2155599603571 | | 1992 | 3.8733753699648 | | 1991 | 5.5555555555558 | | 1990 | 5.8366877515817 | | 1989 | 3.9916280460457 | | 1988 | 3.1218684961072 | | 1987 | 3.6430454581771 | | 1986 | 1.0739664082683 | | 1985 | 4.0322580562863 |
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