| Year | Value | | 2013 | -15.105874482269 | | 2012 | -15.734326145766 | | 2011 | -15.965598601554 | | 2010 | -12.690358518052 | | 2009 | -25.235044582943 | | 2008 | -26.45171574949 | | 2007 | -38.839806413083 | | 2006 | -46.523327446109 | | 2005 | -47.289301206012 | | 2004 | -47.752773551773 | | 2003 | -30.316374582101 | | 2002 | -33.317261425921 | | 2001 | -36.333519864017 | | 2000 | -38.916035395123 | | 1999 | -36.325353206169 | | 1998 | -31.06233617581 | | 1997 | -26.399341349907 | | 1996 | -24.168741905789 | | 1995 | -20.773778338399 | | 1994 | -17.269849066138 | | 1993 | -17.118239337864 | | 1992 | -16.423006471657 | | 1991 | -11.547211767975 | | 1990 | -2.3150565572914 | | 1989 | 2.8681696160235 | | 1988 | 9.2544316646689 | | 1987 | 13.224710601041 | | 1986 | 10.563842853401 | | 1985 | 9.7476892559184 | | 1984 | 11.97655030045 | | 1983 | 7.6690175136281 | | 1982 | 6.056436944772 | | 1981 | 5.0839160013877 | | 1980 | 8.4063423179641 | | 1979 | 4.8584536365295 | | 1978 | 1.2221953084998 | | 1977 | 0.40776616985698 | | 1976 | 0.11908982878654 | | 1975 | 13.525820884286 | | 1974 | 14.898328998901 | | 1973 | 25.73003719268 | | 1972 | 27.991074666825 | | 1971 | 24.48128775801 |
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