| Year | Value | | 2022 | 50.503314618542 | | 2021 | 50.496982251456 | | 2020 | 50.505609000748 | | 2019 | 50.509688392205 | | 2018 | 50.509321608827 | | 2017 | 50.511642291754 | | 2016 | 50.514535298988 | | 2015 | 50.516486986917 | | 2014 | 50.519771554677 | | 2013 | 50.522214369464 | | 2012 | 50.525886881672 | | 2011 | 50.530637506746 | | 2010 | 50.5352792057 | | 2009 | 50.540438013131 | | 2008 | 50.561292517553 | | 2007 | 50.597672250346 | | 2006 | 50.632726653256 | | 2005 | 50.669112177835 | | 2004 | 50.70625291796 | | 2003 | 50.741368079195 | | 2002 | 50.774790736248 | | 2001 | 50.810499625877 | | 2000 | 50.849177739026 | | 1999 | 50.88980541736 | | 1998 | 50.889431957643 | | 1997 | 50.885805789214 | | 1996 | 50.929094204467 | | 1995 | 50.9732471953 | | 1994 | 51.027593762636 | | 1993 | 51.243153008479 | | 1992 | 51.70388800824 | | 1991 | 52.094895955035 | | 1990 | 52.305873945438 | | 1989 | 52.52321568913 | | 1988 | 52.681897220966 | | 1987 | 52.842100722993 | | 1986 | 53.061490602725 | | 1985 | 53.221164600757 | | 1984 | 53.324177984578 | | 1983 | 53.438525234519 | | 1982 | 53.565230080703 | | 1981 | 53.696551732807 | | 1980 | 53.786079243305 | | 1979 | 53.794882454962 | | 1978 | 53.653069108818 | | 1977 | 53.450955324801 | | 1976 | 53.086764454532 | | 1975 | 52.089263222731 | | 1974 | 51.306186471274 | | 1973 | 51.094776106334 | | 1972 | 50.877933236372 | | 1971 | 50.643562049865 | | 1970 | 50.38204374285 | | 1969 | 50.235324657904 | | 1968 | 50.215599954159 | | 1967 | 50.196103755653 | | 1966 | 50.179291754706 | | 1965 | 50.16536949374 | | 1964 | 50.150003799136 | | 1963 | 50.133706930372 | | 1962 | 50.118624515319 | | 1961 | 50.103642693799 | | 1960 | 50.091578793131 |
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