| Year | Value | | 2014 | 7.700382741099 | | 2013 | 6.6190618092159 | | 2012 | 6.2704733238344 | | 2011 | 3.9586117346874 | | 2010 | 4.8052371131225 | | 2009 | 3.8036159119365 | | 2008 | 2.4567329346844 | | 2007 | 2.2217742122825 | | 2006 | 1.2855853104879 | | 2005 | 0.58899508441086 | | 2004 | 0.037092227381147 | | 2003 | -1.5137998758706 | | 2002 | -3.0277321301419 | | 2001 | -5.0178228706548 | | 2000 | -4.4215452110783 | | 1999 | -4.1423696457073 | | 1998 | -5.9229486150883 | | 1997 | -5.4199676226079 | | 1996 | -6.2209161856629 | | 1995 | -6.4020187033657 | | 1994 | -6.9363096658084 | | 1993 | -5.6470396988599 | | 1992 | -8.6266558061544 | | 1991 | -10.222099084298 | | 1990 | -6.668202057707 | | 1989 | -10.993495187719 | | 1988 | -8.2612596278315 | | 1987 | -9.7222834364779 | | 1986 | -12.035166563657 | | 1985 | -12.485235704145 | | 1984 | -12.533039338503 | | 1983 | -9.2910919857542 | | 1982 | -8.1432529514654 | | 1981 | -8.8669482486806 | | 1980 | -8.7963108465392 | | 1979 | -9.047835578023 | | 1978 | -8.552701068084 | | 1977 | -9.2039517326319 | | 1976 | -8.8668581842057 | | 1975 | -7.4509139990057 | | 1974 | -7.9410303186172 | | 1973 | -7.2686831985389 | | 1972 | -5.4824097621072 | | 1971 | -3.9808205094035 |
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