| Year | Value | | 2022 | 50.405959805389 | | 2021 | 50.371290603749 | | 2020 | 50.336137642347 | | 2019 | 50.31307715867 | | 2018 | 50.305389617101 | | 2017 | 50.304131419915 | | 2016 | 50.301810001799 | | 2015 | 50.294544327361 | | 2014 | 50.282535311316 | | 2013 | 50.263588636534 | | 2012 | 50.234981372314 | | 2011 | 50.197526328948 | | 2010 | 50.180831224191 | | 2009 | 50.194565369427 | | 2008 | 50.213809476261 | | 2007 | 50.231516750376 | | 2006 | 50.245656935692 | | 2005 | 50.256031540429 | | 2004 | 50.265509669422 | | 2003 | 50.27669887866 | | 2002 | 50.295015226786 | | 2001 | 50.327206047397 | | 2000 | 50.372402211525 | | 1999 | 50.387813322528 | | 1998 | 50.36717075207 | | 1997 | 50.344470564131 | | 1996 | 50.323393859993 | | 1995 | 50.306136373584 | | 1994 | 50.290113881756 | | 1993 | 50.274169486031 | | 1992 | 50.258395506538 | | 1991 | 50.242786957002 | | 1990 | 50.22834388112 | | 1989 | 50.216637393467 | | 1988 | 50.193632758873 | | 1987 | 50.159386436422 | | 1986 | 50.129092060965 | | 1985 | 50.103815925457 | | 1984 | 50.083776257552 | | 1983 | 50.066738855268 | | 1982 | 50.050426619868 | | 1981 | 50.032342065787 | | 1980 | 50.012486894651 | | 1979 | 49.991794614371 | | 1978 | 49.97648322759 | | 1977 | 49.977170343577 | | 1976 | 49.992217562933 | | 1975 | 50.013091551339 | | 1974 | 50.036864315758 | | 1973 | 50.059936861277 | | 1972 | 50.075632316226 | | 1971 | 50.080020726309 | | 1970 | 50.072804278604 | | 1969 | 50.052976217363 | | 1968 | 50.026088949501 | | 1967 | 50.003880830949 | | 1966 | 49.991421802005 | | 1965 | 49.984657058811 | | 1964 | 49.976042035585 | | 1963 | 49.95919649629 | | 1962 | 50.010092651497 | | 1961 | 50.143153449029 | | 1960 | 50.29455886729 |
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