| Year | Value | | 2016 | 3.4136343219042 | | 2015 | 5.5882846220867 | | 2014 | 2.904526340171 | | 2013 | 2.9475084503397 | | 2012 | 5.1790234613814 | | 2011 | 0.14900717273162 | | 2010 | 7.5053094741438 | | 2009 | 3.6822250991705 | | 2008 | -2.2932777464724 | | 2007 | 3.5615356602224 | | 2006 | 13.801298366153 | | 2005 | 9.1433793248855 | | 2004 | 5.4666285443815 | | 2003 | 5.8107546571297 | | 2002 | 2.3627844974876 | | 2001 | 4.0371307933782 | | 2000 | 2.4324704303488 | | 1999 | 5.1169141076259 | | 1998 | -1.1089969115265 | | 1997 | 2.2401976735749 | | 1996 | 6.9614655436371 | | 1995 | -1.9488720150352 | | 1994 | 1.5107712772794 | | 1993 | -12.233780378583 | | 1992 | -16.544356850316 | | 1991 | -10.053511394997 | | 1990 | 0.44991494966163 | | 1989 | 0.85687648428248 | | 1988 | 4.8800778837919 | | 1987 | 0.95055381533692 | | 1986 | -4.5511793588262 | | 1985 | 3.3369496592153 | | 1984 | 7.884341886739 | | 1983 | 5.3326975088963 | | 1982 | 8.7074322674386 | | 1981 | 18.735719659761 | | 1980 | -4.9642418627154 | | 1979 | 0.92133479685638 | | 1978 | 6.5823872887666 | | 1977 | 8.5859660309143 | | 1976 | 5.3158780457579 | | 1975 | 8.9175515374072 | | 1974 | 0.89365066230691 | | 1973 | 3.4121642994754 | | 1972 | 4.7885161168979 | | 1971 | 8.5288288149306 |
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