| Year | Value | | 2014 | -14.8995881431 | | 2013 | -18.918738075292 | | 2012 | -14.18641290691 | | 2011 | -23.024166105747 | | 2010 | -3.7374780391076 | | 2009 | 4.2431783448963 | | 2008 | 15.935571056167 | | 2007 | 12.971325874588 | | 2006 | 12.070384276538 | | 2005 | 20.010212006502 | | 2004 | 25.379457706186 | | 2003 | 18.318353050172 | | 2002 | 21.753024575521 | | 2001 | 20.191085048981 | | 2000 | 23.408711478662 | | 1999 | 22.269879012832 | | 1998 | 14.938434730489 | | 1997 | 10.916223231982 | | 1996 | 11.865159160553 | | 1995 | 8.665523855254 | | 1994 | 1.5829441959687 | | 1993 | -1.5722153260986 | | 1992 | -3.3420315602095 | | 1991 | -2.9374541107884 | | 1990 | -8.854998297252 | | 1989 | -7.4071562665475 | | 1988 | -6.2356585890216 | | 1987 | -16.621915822981 | | 1986 | -29.337272797633 | | 1985 | -38.586754131631 | | 1984 | -34.599246109733 | | 1983 | -28.08997124494 | | 1982 | -29.609408074068 | | 1981 | -28.612249412869 | | 1980 | -28.536047243527 | | 1979 | -34.663904848967 | | 1978 | -16.20853047413 | | 1977 | 15.288835609826 | | 1976 | 20.517252068434 | | 1975 | 22.267184661262 | | 1974 | 17.546206527799 | | 1973 | 17.226332014181 | | 1972 | 17.597788032969 | | 1971 | 19.433030682245 |
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