| Year | Value | | 2022 | 50.472936428965 | | 2021 | 50.49341844853 | | 2020 | 50.516195266298 | | 2019 | 50.54235154746 | | 2018 | 50.569883774441 | | 2017 | 50.598557059403 | | 2016 | 50.626901067322 | | 2015 | 50.654048273843 | | 2014 | 50.682047621541 | | 2013 | 50.707526910375 | | 2012 | 50.730800759017 | | 2011 | 50.756886662191 | | 2010 | 50.785350739453 | | 2009 | 50.814318622002 | | 2008 | 50.844730140044 | | 2007 | 50.876671340789 | | 2006 | 50.907932572179 | | 2005 | 50.940429651019 | | 2004 | 50.975547706992 | | 2003 | 51.008949586898 | | 2002 | 51.03746747418 | | 2001 | 51.060865210952 | | 2000 | 51.080595205043 | | 1999 | 51.098388190993 | | 1998 | 51.115932276548 | | 1997 | 51.13156390509 | | 1996 | 51.146201909384 | | 1995 | 51.15841331521 | | 1994 | 51.172140391804 | | 1993 | 51.194597450192 | | 1992 | 51.217404605455 | | 1991 | 51.234252158617 | | 1990 | 51.244752405663 | | 1989 | 51.248436228513 | | 1988 | 51.24582737569 | | 1987 | 51.239340947938 | | 1986 | 51.211285838327 | | 1985 | 51.159162745451 | | 1984 | 51.093005965818 | | 1983 | 51.010989440388 | | 1982 | 50.919895689152 | | 1981 | 50.8303352262 | | 1980 | 50.742372831851 | | 1979 | 50.66505342846 | | 1978 | 50.602649236549 | | 1977 | 50.547167237989 | | 1976 | 50.498425641958 | | 1975 | 50.447802264078 | | 1974 | 50.388058949261 | | 1973 | 50.325355983291 | | 1972 | 50.258916327984 | | 1971 | 50.182190883523 | | 1970 | 50.117047124746 | | 1969 | 50.064447941273 | | 1968 | 50.010457521732 | | 1967 | 49.954489477328 | | 1966 | 49.895016256911 | | 1965 | 49.832292376444 | | 1964 | 49.768650708631 | | 1963 | 49.703555992513 | | 1962 | 49.634581379105 | | 1961 | 49.561251983813 | | 1960 | 49.483062312658 |
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