| Year | Value | | 2015 | 31.119059660162 | | 2014 | -7.3474344662706 | | 2013 | -10.549752581497 | | 2012 | -11.362116716509 | | 2011 | -13.846285849127 | | 2010 | -15.553327533791 | | 2009 | -17.054287356234 | | 2008 | -18.967170552462 | | 2007 | -20.188239331287 | | 2006 | -22.080652233054 | | 2005 | -23.507120109715 | | 2004 | -23.919010153096 | | 2003 | -24.190545425405 | | 2002 | -24.523520563307 | | 2001 | -25.692324801761 | | 2000 | -25.817679691065 | | 1999 | -24.413263675333 | | 1998 | -25.611480455302 | | 1997 | -24.218840096376 | | 1996 | -23.298398193121 | | 1995 | -22.637449249599 | | 1994 | -22.859122859261 | | 1993 | -21.259322918722 | | 1992 | -21.869629226639 | | 1991 | -21.274597120919 | | 1990 | -23.292699452444 | | 1989 | -27.259926429108 | | 1988 | -25.339654195637 | | 1987 | -23.76407548937 | | 1986 | -24.013167799246 | | 1985 | -25.846536071397 | | 1984 | -26.468729092273 | | 1983 | -24.516905493729 | | 1982 | -23.242250362715 | | 1981 | -21.515035235845 | | 1980 | -29.285021342914 | | 1979 | -39.000823030352 | | 1978 | -41.047268252452 | | 1977 | -44.638022807502 | | 1976 | -47.865872941247 | | 1975 | -45.230754453406 | | 1974 | -53.658097343377 | | 1973 | -59.048245372235 | | 1972 | -55.636247892816 | | 1971 | -57.528547199561 | | 1970 | -8.1242822755628 | | 1969 | -9.1343594327208 | | 1968 | -9.8337016679542 | | 1967 | -9.9973017439802 | | 1966 | -10.977536992129 | | 1965 | -11.365583137978 | | 1964 | -13.024583773281 | | 1963 | -11.124620546235 | | 1962 | -9.3189938288305 | | 1961 | -12.839164755051 | | 1960 | -14.359811407812 |
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