| Year | Value | | 2022 | 49.541166059629 | | 2021 | 49.554887904378 | | 2020 | 49.568769623031 | | 2019 | 49.590606623177 | | 2018 | 49.60885262936 | | 2017 | 49.615832972044 | | 2016 | 49.636156353658 | | 2015 | 49.672026350408 | | 2014 | 49.719429427027 | | 2013 | 49.772057532592 | | 2012 | 49.838814310898 | | 2011 | 49.933290414714 | | 2010 | 50.017189049481 | | 2009 | 50.07207199372 | | 2008 | 50.141549376407 | | 2007 | 50.25158310396 | | 2006 | 50.353318871757 | | 2005 | 50.402914209844 | | 2004 | 50.422306842553 | | 2003 | 50.4346281308 | | 2002 | 50.441936190381 | | 2001 | 50.44870234206 | | 2000 | 50.473214074985 | | 1999 | 50.506483209185 | | 1998 | 50.527701032296 | | 1997 | 50.543012298957 | | 1996 | 50.552047125306 | | 1995 | 50.55181606911 | | 1994 | 50.549156866484 | | 1993 | 50.54332701937 | | 1992 | 50.543151531637 | | 1991 | 50.555317528437 | | 1990 | 50.555752544537 | | 1989 | 50.538126372995 | | 1988 | 50.536992003854 | | 1987 | 50.558915662535 | | 1986 | 50.564312690299 | | 1985 | 50.554165943231 | | 1984 | 50.537131346409 | | 1983 | 50.513712731666 | | 1982 | 50.495500410578 | | 1981 | 50.470760551288 | | 1980 | 50.44287792576 | | 1979 | 50.421236476567 | | 1978 | 50.399513945847 | | 1977 | 50.373562983864 | | 1976 | 50.349947867951 | | 1975 | 50.32736397514 | | 1974 | 50.307498908511 | | 1973 | 50.291399847856 | | 1972 | 50.274812378291 | | 1971 | 50.26797953322 | | 1970 | 50.257666919706 | | 1969 | 50.240011685446 | | 1968 | 50.227288330209 | | 1967 | 50.2214651847 | | 1966 | 50.20680364405 | | 1965 | 50.188746639595 | | 1964 | 50.186552368775 | | 1963 | 50.186893203883 | | 1962 | 50.183326633019 | | 1961 | 50.181371442343 | | 1960 | 50.181235899841 |
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