| Year | Value | | 2022 | 50.072331389355 | | 2021 | 50.08888188803 | | 2020 | 50.10286389351 | | 2019 | 50.123421187247 | | 2018 | 50.15842738572 | | 2017 | 50.214284890256 | | 2016 | 50.270730424801 | | 2015 | 50.317653916043 | | 2014 | 50.366047981111 | | 2013 | 50.414129332394 | | 2012 | 50.455487156997 | | 2011 | 50.47836336822 | | 2010 | 50.484629858682 | | 2009 | 50.490351038749 | | 2008 | 50.491586150527 | | 2007 | 50.502958386959 | | 2006 | 50.52934567908 | | 2005 | 50.545124380655 | | 2004 | 50.550057849458 | | 2003 | 50.55920168782 | | 2002 | 50.572677579455 | | 2001 | 50.585989387341 | | 2000 | 50.600288674263 | | 1999 | 50.614975560651 | | 1998 | 50.627507089752 | | 1997 | 50.638307902094 | | 1996 | 50.648849582623 | | 1995 | 50.658702129815 | | 1994 | 50.67166926699 | | 1993 | 50.686190354479 | | 1992 | 50.698093385078 | | 1991 | 50.710941184911 | | 1990 | 50.723539599819 | | 1989 | 50.733968655895 | | 1988 | 50.743598347952 | | 1987 | 50.752554691663 | | 1986 | 50.760289665416 | | 1985 | 50.766716320748 | | 1984 | 50.773926465496 | | 1983 | 50.782652689081 | | 1982 | 50.815455851345 | | 1981 | 50.859068183386 | | 1980 | 50.885216397343 | | 1979 | 50.906554977143 | | 1978 | 50.92518041346 | | 1977 | 50.938455133085 | | 1976 | 50.948042274755 | | 1975 | 50.95727349387 | | 1974 | 50.967197481373 | | 1973 | 50.993500891175 | | 1972 | 51.020899029392 | | 1971 | 51.03376510241 | | 1970 | 51.051770960212 | | 1969 | 51.075242777226 | | 1968 | 51.100805636666 | | 1967 | 51.130640227868 | | 1966 | 51.159192804479 | | 1965 | 51.183814474604 | | 1964 | 51.2086269707 | | 1963 | 51.235767539535 | | 1962 | 51.264669320398 | | 1961 | 51.293876882708 | | 1960 | 51.31793093995 |
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