| Year | Value | | 2015 | -72.528169765865 | | 2014 | -67.927221743038 | | 2013 | -64.443748051102 | | 2012 | -59.114160400191 | | 2011 | -52.962078916313 | | 2010 | -51.374873798441 | | 2009 | -50.19771512577 | | 2008 | -50.428256041537 | | 2007 | -53.291717576343 | | 2006 | -53.809492296482 | | 2005 | -48.953644870421 | | 2004 | -48.23775636839 | | 2003 | -47.046452799055 | | 2002 | -54.124094126959 | | 2001 | -51.668195278346 | | 2000 | -47.804356415709 | | 1999 | -48.735676090585 | | 1998 | -53.536082803912 | | 1997 | -52.383901118203 | | 1996 | -51.268419959807 | | 1995 | -50.505881068043 | | 1994 | -47.835757214191 | | 1993 | -42.892386217409 | | 1992 | -37.540384782512 | | 1991 | -36.560282500619 | | 1990 | -30.835755236888 | | 1989 | -26.148215448833 | | 1988 | -29.11820148297 | | 1987 | -24.554389083384 | | 1986 | -22.092200662907 | | 1985 | -24.998445526685 | | 1984 | -21.212278162041 | | 1983 | -15.420002961233 | | 1982 | -12.345262194916 | | 1981 | -6.8749072534919 | | 1980 | -7.9348745215586 | | 1979 | -10.435063763229 | | 1978 | -5.4373464010481 | | 1977 | -7.7100299065588 | | 1976 | -6.4866793526634 | | 1975 | -13.018307809907 | | 1974 | -18.651296004848 | | 1973 | -24.396253842336 | | 1972 | -15.94964271134 | | 1971 | -10.248718652922 | | 1970 | -4.8221998631466 | | 1969 | 2.004650070445 | | 1968 | 7.020185474869 | | 1967 | 8.2594778868004 | | 1966 | 8.3881747083161 | | 1965 | 11.536018438818 | | 1964 | 10.00630979328 | | 1963 | 11.421954339718 | | 1962 | 10.515045979223 | | 1961 | 18.368620151145 | | 1960 | 25.01942237122 |
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