| Year | Value | | 2014 | 1.9592673013969 | | 2013 | 0.22473173304266 | | 2012 | -1.5471374201009 | | 2011 | -2.1167562382451 | | 2010 | -2.8703535435954 | | 2009 | -3.4370854509967 | | 2008 | -3.4638908564897 | | 2007 | -4.605349707315 | | 2006 | -5.2157546036619 | | 2005 | -5.9811940639946 | | 2004 | -7.4097476631535 | | 2003 | -7.1189078438121 | | 2002 | -6.9261403140866 | | 2001 | -7.7524708252689 | | 2000 | -7.2154727970477 | | 1999 | -6.5856024595524 | | 1998 | -5.4797444246385 | | 1997 | -5.9603499790896 | | 1996 | -6.2189006369511 | | 1995 | -6.2843858975429 | | 1994 | -6.0346917360754 | | 1993 | -2.9105540082488 | | 1992 | -2.9339456732089 | | 1991 | -2.8504200172527 | | 1990 | -1.8684751927327 | | 1989 | -4.0677803761424 | | 1988 | -3.705438793987 | | 1987 | -5.487745312413 | | 1986 | -7.4800373253232 | | 1985 | -7.0838802344769 | | 1984 | -3.3038785945868 | | 1983 | -1.9530480113394 | | 1982 | -4.1654846383544 | | 1981 | 0.67760195389344 | | 1980 | -1.3648606094023 | | 1979 | 0.64479798509862 | | 1978 | 0.79283056863228 | | 1977 | -4.2247121968813 | | 1976 | -6.1789553853199 | | 1975 | 11.161527804734 | | 1974 | 12.046892523278 | | 1973 | 11.400975326598 | | 1972 | 11.050519483647 | | 1971 | 11.187984667611 |
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