| Year | Value | | 2015 | 75.207880041183 | | 2014 | -53.259184922823 | | 2013 | -52.809262216994 | | 2012 | -47.331125310059 | | 2011 | -47.831469648435 | | 2010 | -50.832808144355 | | 2009 | -51.801258135193 | | 2008 | -48.478761891813 | | 2007 | -47.306877772248 | | 2006 | -46.006798467808 | | 2005 | -46.511300669483 | | 2004 | -43.275494752073 | | 2003 | -38.937531336588 | | 2002 | -35.644626551656 | | 2001 | -32.321594297493 | | 2000 | -28.79181031573 | | 1999 | -26.166415906727 | | 1998 | -24.29624393433 | | 1997 | -21.361105138171 | | 1996 | -20.649355982716 | | 1995 | -19.087895268199 | | 1994 | -19.061909403604 | | 1993 | -14.162580488595 | | 1992 | -13.399578117783 | | 1991 | -10.680859538446 | | 1990 | -15.250465667038 | | 1989 | 53.054971368211 | | 1988 | 53.147710554532 | | 1987 | 52.767977583902 | | 1986 | 52.223763491137 | | 1985 | 52.930383491817 | | 1984 | 52.829309721567 | | 1983 | 53.749729085972 | | 1982 | 52.990654358766 | | 1981 | 53.30455583238 | | 1980 | 54.979026715951 | | 1979 | 53.67476607162 | | 1978 | 54.787453788769 | | 1977 | 55.696395104556 | | 1976 | 53.169269607912 | | 1975 | 51.282851143381 | | 1974 | 50.906198437388 | | 1973 | 48.463865966229 | | 1972 | 45.420142200271 | | 1971 | 45.503111254153 | | 1970 | 23.184991572491 | | 1969 | 19.435914726701 | | 1968 | 18.088274208953 | | 1967 | 16.256700210398 | | 1966 | 19.350595763956 | | 1965 | 18.820090522769 | | 1964 | 19.243570633854 | | 1963 | 18.026198345036 | | 1962 | 17.941880543195 | | 1961 | 12.586700771082 | | 1960 | 12.335653942187 |
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