| Year | Value | | 2014 | -33.487566231273 | | 2013 | -37.417273799621 | | 2012 | -37.304964689955 | | 2011 | -45.486110617613 | | 2010 | -51.031884189294 | | 2009 | -52.93959345317 | | 2008 | -58.583852304105 | | 2007 | -57.320639177107 | | 2006 | -49.320733133207 | | 2005 | -47.227358286775 | | 2004 | -39.999828679806 | | 2003 | -36.647171503757 | | 2002 | -38.451310629356 | | 2001 | -34.273454414378 | | 2000 | -35.801465213098 | | 1999 | -30.61239944315 | | 1998 | -28.703656275843 | | 1997 | -27.547303644157 | | 1996 | -27.451880344324 | | 1995 | -25.951368556382 | | 1994 | -26.958683850879 | | 1993 | -21.54602105388 | | 1992 | -21.900492581236 | | 1991 | -21.834085920297 | | 1990 | -20.207867364508 | | 1989 | -20.122349130876 | | 1988 | -19.740919307533 | | 1987 | -10.012077098266 | | 1986 | -6.2413830083684 | | 1985 | -4.0099776266014 | | 1984 | -2.5346580957295 | | 1983 | 0.7993743570137 | | 1982 | 1.508238677077 | | 1981 | 1.5112444270215 | | 1980 | 1.0727466807148 | | 1979 | 0.31168561841422 | | 1978 | 1.1591653276806 | | 1977 | 0.38235793919833 | | 1976 | -1.00719278165 | | 1975 | 0.053839673602831 | | 1974 | 0.24907011100768 | | 1973 | 0.75161892785152 | | 1972 | 1.4126154598343 | | 1971 | 3.5638457159137 |
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