| Year | Value | | 2021 | 65.039236835374 | | 2020 | 65.367781754362 | | 2019 | 65.818219295172 | | 2018 | 65.436056859975 | | 2017 | 64.956696967611 | | 2016 | 64.499765156003 | | 2015 | 63.914282460028 | | 2014 | 63.46874282905 | | 2013 | 63.063742857029 | | 2012 | 62.545773344407 | | 2011 | 62.159695393228 | | 2010 | 61.526592770602 | | 2009 | 61.029019581777 | | 2008 | 60.223179915829 | | 2007 | 59.623664090112 | | 2006 | 58.877158467519 | | 2005 | 58.0271410652 | | 2004 | 57.369815340281 | | 2003 | 56.88742997928 | | 2002 | 55.769914713671 | | 2001 | 55.284455640442 | | 2000 | 54.819907231808 | | 1999 | 54.242470157783 | | 1998 | 53.140174307501 | | 1997 | 53.269260274601 | | 1996 | 52.835320247312 | | 1995 | 52.698629612286 | | 1994 | 52.9300987588 | | 1993 | 52.459747937712 | | 1992 | 51.639181394416 | | 1991 | 51.712008656103 | | 1990 | 51.902396454139 | | 1989 | 51.727935386917 | | 1988 | 50.370421059643 | | 1987 | 50.826569100231 | | 1986 | 50.00460612637 | | 1985 | 49.083237492252 | | 1984 | 48.752529523901 | | 1983 | 48.698525093977 | | 1982 | 50.073435739892 | | 1981 | 49.826901268242 | | 1980 | 49.563056533782 | | 1979 | 49.157426532422 | | 1978 | 48.712014707526 | | 1977 | 48.382229539316 | | 1976 | 48.043508606355 | | 1975 | 47.250468551984 | | 1974 | 46.988665205722 | | 1973 | 46.979038808228 | | 1972 | 46.299719110264 | | 1971 | 46.497570315894 | | 1970 | 45.995730793558 | | 1969 | 45.680652497825 | | 1968 | 45.378519522557 | | 1967 | 45.029736243152 | | 1966 | 44.228213717936 | | 1965 | 44.450467202143 | | 1964 | 44.359479985062 | | 1963 | 43.719840932642 | | 1962 | 43.431420340743 | | 1961 | 43.083039373549 | | 1960 | 42.679277237944 |
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