| Year | Value | | 2021 | 47.092932752179 | | 2020 | 47.637764632628 | | 2019 | 47.118877127439 | | 2018 | 47.936124948111 | | 2017 | 48.00098588626 | | 2016 | 47.729867164799 | | 2015 | 46.961913657119 | | 2014 | 47.026774595268 | | 2013 | 47.063096720631 | | 2012 | 46.781600249066 | | 2011 | 46.616853466169 | | 2010 | 45.716583644666 | | 2009 | 45.76198630137 | | 2008 | 45.808686176837 | | 2007 | 46.716739310917 | | 2006 | 46.875 | | 2005 | 46.654472810295 | | 2004 | 46.758250311333 | | 2003 | 47.792133665421 | | 2002 | 47.846616853466 | | 2001 | 47.960772104608 | | 2000 | 47.605334163553 | | 1999 | 47.680572851806 | | 1998 | 47.685761726858 | | 1997 | 47.567714819427 | | 1996 | 46.92299709423 | | 1995 | 46.733603154836 | | 1994 | 46.427459526775 | | 1993 | 46.375570776256 | | 1992 | 45.895599833956 | | 1991 | 45.752905770029 | | 1990 | 45.669883769199 | | 1989 | 46.518264840183 | | 1988 | 45.852791614778 | | 1987 | 47.570309256953 | | 1986 | 46.143368617684 | | 1985 | 48.150166044002 | | 1984 | 48.645703611457 | | 1983 | 47.230437941054 | | 1982 | 49.954597343296 | | 1981 | 47.353673723537 | | 1980 | 48.536737235367 | | 1979 | 47.13703819012 | | 1978 | 47.240815691158 | | 1977 | 46.58701743462 | | 1976 | 46.326276463263 | | 1975 | 46.745278123703 | | 1974 | 46.362598588626 | | 1973 | 47.218762972188 | | 1972 | 46.057752179328 | | 1971 | 46.031807804068 | | 1970 | 46.524750933998 | | 1969 | 46.310709838107 | | 1968 | 48.217621419676 | | 1967 | 48.606787048568 | | 1966 | 48.535440016604 | | 1965 | 48.301940639269 | | 1964 | 47.160388127854 | | 1963 | 46.544209215442 | | 1962 | 46.492320464923 | | 1961 | 46.349626400996 |
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