| Year | Value | | 2022 | 50.040635154818 | | 2021 | 50.032770026885 | | 2020 | 50.024493942969 | | 2019 | 50.020753891476 | | 2018 | 50.02331925693 | | 2017 | 50.02471069486 | | 2016 | 50.022420345618 | | 2015 | 50.013869405036 | | 2014 | 50.003573476423 | | 2013 | 49.994506599523 | | 2012 | 49.98312547404 | | 2011 | 49.969112921027 | | 2010 | 49.954999658037 | | 2009 | 49.942416604013 | | 2008 | 49.932891666946 | | 2007 | 49.927234421751 | | 2006 | 49.924820306476 | | 2005 | 49.92627784535 | | 2004 | 49.936803702454 | | 2003 | 49.953778876043 | | 2002 | 49.971754206473 | | 2001 | 49.991209359626 | | 2000 | 50.016906344389 | | 1999 | 50.047133022918 | | 1998 | 50.072418942749 | | 1997 | 50.092567041426 | | 1996 | 50.110611445719 | | 1995 | 50.124406078883 | | 1994 | 50.131364290079 | | 1993 | 50.132328662997 | | 1992 | 50.116211967887 | | 1991 | 50.083262536215 | | 1990 | 50.047387883824 | | 1989 | 50.010689998887 | | 1988 | 49.972663304359 | | 1987 | 49.931226696622 | | 1986 | 49.886050695668 | | 1985 | 49.839195168121 | | 1984 | 49.79277454985 | | 1983 | 49.74623760928 | | 1982 | 49.699506615909 | | 1981 | 49.653261255358 | | 1980 | 49.607280407652 | | 1979 | 49.562748848618 | | 1978 | 49.518625521419 | | 1977 | 49.472433917884 | | 1976 | 49.424622801758 | | 1975 | 49.373216315959 | | 1974 | 49.31970755061 | | 1973 | 49.265322482699 | | 1972 | 49.21159120356 | | 1971 | 49.160177912583 | | 1970 | 49.108056947085 | | 1969 | 49.055459540065 | | 1968 | 49.000408467713 | | 1967 | 48.941504841276 | | 1966 | 48.879106639915 | | 1965 | 48.81092933374 | | 1964 | 48.741118575074 | | 1963 | 48.671692680935 | | 1962 | 48.59814242226 | | 1961 | 48.519992066312 | | 1960 | 48.442287917876 |
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