| Year | Value | | 2015 | 31.119059660162 | | 2014 | -6.4683684718397 | | 2013 | -9.7842213339413 | | 2012 | -10.476500051611 | | 2011 | -12.699107762724 | | 2010 | -14.36698263682 | | 2009 | -16.292501076562 | | 2008 | -18.316950777723 | | 2007 | -19.410077232674 | | 2006 | -21.281161639633 | | 2005 | -22.675095974167 | | 2004 | -23.00783675482 | | 2003 | -23.24752268339 | | 2002 | -23.976415425957 | | 2001 | -24.756508240478 | | 2000 | -24.966515948088 | | 1999 | -23.85680181825 | | 1998 | -25.022420533976 | | 1997 | -23.237525198451 | | 1996 | -22.418821449339 | | 1995 | -21.758179204581 | | 1994 | -22.032106784339 | | 1993 | -20.634822478838 | | 1992 | -21.437516170607 | | 1991 | -20.954193527029 | | 1990 | -23.309106640115 | | 1989 | -26.405484272234 | | 1988 | -24.915134112445 | | 1987 | -23.712284592494 | | 1986 | -23.625626915091 | | 1985 | -25.471536370115 | | 1984 | -26.341061008944 | | 1983 | -24.675448742703 | | 1982 | -23.049526158066 | | 1981 | -20.474449686914 | | 1980 | -27.230160261422 | | 1979 | -37.221841746976 | | 1978 | -40.478743415312 | | 1977 | -43.63470061179 | | 1976 | -46.851597784776 | | 1975 | -44.758334680109 | | 1974 | -52.322789217176 | | 1973 | -58.951971819602 | | 1972 | -55.804790829218 | | 1971 | -59.208272753894 | | 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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