| Year | Value | | 2022 | 49.308679160488 | | 2021 | 49.344722325941 | | 2020 | 49.380272270285 | | 2019 | 49.412510732643 | | 2018 | 49.440126109616 | | 2017 | 49.467036264396 | | 2016 | 49.495135291376 | | 2015 | 49.522368969488 | | 2014 | 49.54891716127 | | 2013 | 49.575382488915 | | 2012 | 49.599804460929 | | 2011 | 49.624485708688 | | 2010 | 49.653245852587 | | 2009 | 49.686686439539 | | 2008 | 49.723207314664 | | 2007 | 49.759165863886 | | 2006 | 49.791068236284 | | 2005 | 49.818925827949 | | 2004 | 49.844607239399 | | 2003 | 49.868554501988 | | 2002 | 49.892299014889 | | 2001 | 49.915855418225 | | 2000 | 49.953204543025 | | 1999 | 50.002447293998 | | 1998 | 50.051302222817 | | 1997 | 50.102722635374 | | 1996 | 50.156327022827 | | 1995 | 50.210264202854 | | 1994 | 50.262343297933 | | 1993 | 50.312816566836 | | 1992 | 50.361665269229 | | 1991 | 50.410637359533 | | 1990 | 50.431811719818 | | 1989 | 50.421603010694 | | 1988 | 50.407298488251 | | 1987 | 50.389947224258 | | 1986 | 50.371501056757 | | 1985 | 50.353637124928 | | 1984 | 50.336136197664 | | 1983 | 50.323046092184 | | 1982 | 50.317930939182 | | 1981 | 50.317640520227 | | 1980 | 50.322715776576 | | 1979 | 50.334668746024 | | 1978 | 50.352168582955 | | 1977 | 50.376846151655 | | 1976 | 50.407036035576 | | 1975 | 50.437356184678 | | 1974 | 50.462394780665 | | 1973 | 50.48014255207 | | 1972 | 50.501618198764 | | 1971 | 50.533112063931 | | 1970 | 50.564078471055 | | 1969 | 50.591350677988 | | 1968 | 50.621392730906 | | 1967 | 50.65649075391 | | 1966 | 50.694934031624 | | 1965 | 50.73303384531 | | 1964 | 50.768640232734 | | 1963 | 50.802340791738 | | 1962 | 50.817528901612 | | 1961 | 50.796473963675 | | 1960 | 50.754341397671 |
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