| Year | Value | | 2022 | 50.767387461901 | | 2021 | 50.783785667964 | | 2020 | 50.797477305505 | | 2019 | 50.811064038721 | | 2018 | 50.819562167942 | | 2017 | 50.832771052127 | | 2016 | 50.867310853894 | | 2015 | 50.98122389548 | | 2014 | 51.114653221728 | | 2013 | 51.183914597244 | | 2012 | 51.234602391538 | | 2011 | 51.278398798741 | | 2010 | 51.304265578072 | | 2009 | 51.319146079887 | | 2008 | 51.334908680082 | | 2007 | 51.344264461184 | | 2006 | 51.356092331142 | | 2005 | 51.389249151031 | | 2004 | 51.43490865559 | | 2003 | 51.471101847957 | | 2002 | 51.513468511913 | | 2001 | 51.576802204481 | | 2000 | 51.634669208687 | | 1999 | 51.675274486487 | | 1998 | 51.706561623057 | | 1997 | 51.728930489452 | | 1996 | 51.745335315563 | | 1995 | 51.761303467242 | | 1994 | 51.79011929508 | | 1993 | 51.845640343072 | | 1992 | 51.921968325746 | | 1991 | 52.016842457062 | | 1990 | 52.133093901348 | | 1989 | 52.245002258054 | | 1988 | 52.331752015919 | | 1987 | 52.40180762191 | | 1986 | 52.466510942948 | | 1985 | 52.529451420595 | | 1984 | 52.579954681862 | | 1983 | 52.619739625432 | | 1982 | 52.65020262732 | | 1981 | 52.698208745181 | | 1980 | 52.751345765871 | | 1979 | 52.766333562151 | | 1978 | 52.761793956786 | | 1977 | 52.766033539518 | | 1976 | 52.777671639534 | | 1975 | 52.756342083848 | | 1974 | 52.704938640495 | | 1973 | 52.71111387716 | | 1972 | 52.776284304708 | | 1971 | 52.837838720892 | | 1970 | 52.887378553122 | | 1969 | 52.929405951401 | | 1968 | 52.964131253466 | | 1967 | 53.016664339182 | | 1966 | 53.101464257259 | | 1965 | 53.186170130819 | | 1964 | 53.254676099628 | | 1963 | 53.306987668623 | | 1962 | 53.353985226752 | | 1961 | 53.392106483229 | | 1960 | 53.420644107835 |
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