| Year | Value | | 2022 | 50.235427965018 | | 2021 | 50.230092803895 | | 2020 | 50.225759955146 | | 2019 | 50.206451188769 | | 2018 | 50.172675196731 | | 2017 | 50.138118645492 | | 2016 | 50.118327812262 | | 2015 | 50.112980268852 | | 2014 | 50.102153336356 | | 2013 | 50.086003148444 | | 2012 | 50.064348560301 | | 2011 | 50.037234860187 | | 2010 | 50.004725436874 | | 2009 | 49.96630313482 | | 2008 | 49.922156735031 | | 2007 | 49.872831695302 | | 2006 | 49.819071276656 | | 2005 | 49.760327190083 | | 2004 | 49.693368711219 | | 2003 | 49.663936295231 | | 2002 | 49.668632512114 | | 2001 | 49.672564222872 | | 2000 | 49.693344114107 | | 1999 | 49.731499896475 | | 1998 | 49.76538833512 | | 1997 | 49.787241625795 | | 1996 | 49.806995112161 | | 1995 | 49.824086323797 | | 1994 | 49.84033049054 | | 1993 | 49.855175063347 | | 1992 | 49.867988255811 | | 1991 | 49.896558039419 | | 1990 | 49.936792393747 | | 1989 | 49.96663361806 | | 1988 | 49.993383488127 | | 1987 | 50.023306381917 | | 1986 | 50.061129127511 | | 1985 | 50.108079329163 | | 1984 | 50.164905487005 | | 1983 | 50.231231239663 | | 1982 | 50.306437345305 | | 1981 | 50.37900978147 | | 1980 | 50.416656514218 | | 1979 | 50.407232422679 | | 1978 | 50.373776539433 | | 1977 | 50.336070192385 | | 1976 | 50.30192860358 | | 1975 | 50.269608193232 | | 1974 | 50.240137789407 | | 1973 | 50.218406843414 | | 1972 | 50.203562241644 | | 1971 | 50.195129001951 | | 1970 | 50.186300035898 | | 1969 | 50.176693417852 | | 1968 | 50.164151132099 | | 1967 | 50.153128775282 | | 1966 | 50.132881127233 | | 1965 | 50.094212776648 | | 1964 | 50.052452946621 | | 1963 | 50.010651380322 | | 1962 | 49.966671110519 | | 1961 | 49.919694688773 | | 1960 | 49.869131443352 |
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