| Year | Value | | 2022 | 50.325427596726 | | 2021 | 50.358872717464 | | 2020 | 50.414522162015 | | 2019 | 50.468497959958 | | 2018 | 50.502140172399 | | 2017 | 50.534975030545 | | 2016 | 50.566096016537 | | 2015 | 50.599483265666 | | 2014 | 50.633568695797 | | 2013 | 50.663857195877 | | 2012 | 50.693542958796 | | 2011 | 50.7247251719 | | 2010 | 50.751038476699 | | 2009 | 50.771053590959 | | 2008 | 50.780391561694 | | 2007 | 50.785673968063 | | 2006 | 50.78427205101 | | 2005 | 50.772365140181 | | 2004 | 50.756688861247 | | 2003 | 50.739051932552 | | 2002 | 50.717567958269 | | 2001 | 50.691538099601 | | 2000 | 50.684820336105 | | 1999 | 50.787587992045 | | 1998 | 50.979489245764 | | 1997 | 51.174107432126 | | 1996 | 51.378882313922 | | 1995 | 51.600996708729 | | 1994 | 51.825923445818 | | 1993 | 52.049937818209 | | 1992 | 52.276616401137 | | 1991 | 52.506412579313 | | 1990 | 52.706074654824 | | 1989 | 52.774401697125 | | 1988 | 52.726575943612 | | 1987 | 52.652791745676 | | 1986 | 52.562332302961 | | 1985 | 52.464407459394 | | 1984 | 52.360011486237 | | 1983 | 52.241175136688 | | 1982 | 52.10303901402 | | 1981 | 51.955909239452 | | 1980 | 51.865150608418 | | 1979 | 52.030800630856 | | 1978 | 52.381988458992 | | 1977 | 52.720976889541 | | 1976 | 53.075105817502 | | 1975 | 53.436940831139 | | 1974 | 53.805135160127 | | 1973 | 54.184016824395 | | 1972 | 54.576307708883 | | 1971 | 54.973758355892 | | 1970 | 55.394110985277 | | 1969 | 55.887859107403 | | 1968 | 56.438868377114 | | 1967 | 57.007666506948 | | 1966 | 57.582530319129 | | 1965 | 58.165846364713 | | 1964 | 58.762925935819 | | 1963 | 59.369317886644 | | 1962 | 59.985148252267 | | 1961 | 60.613485305863 | | 1960 | 61.249896371625 |
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