| Year | Value | | 2022 | 50.914465497745 | | 2021 | 50.924124646835 | | 2020 | 50.936824838891 | | 2019 | 50.946529719636 | | 2018 | 50.951891223717 | | 2017 | 50.955452117929 | | 2016 | 50.958492641263 | | 2015 | 50.962631862901 | | 2014 | 50.969165045931 | | 2013 | 50.975726031461 | | 2012 | 50.981489463807 | | 2011 | 50.986244053361 | | 2010 | 50.988567044091 | | 2009 | 50.991368715745 | | 2008 | 50.99441150477 | | 2007 | 50.996216523819 | | 2006 | 50.997105435369 | | 2005 | 50.99546101262 | | 2004 | 50.993676258881 | | 2003 | 50.992696098872 | | 2002 | 50.994558176939 | | 2001 | 51.001123842725 | | 2000 | 51.010223651495 | | 1999 | 51.020749531332 | | 1998 | 51.035516918684 | | 1997 | 50.976788564241 | | 1996 | 50.842415329447 | | 1995 | 50.78485436945 | | 1994 | 50.799631141576 | | 1993 | 50.809478880617 | | 1992 | 50.817388303101 | | 1991 | 50.824513213773 | | 1990 | 50.828287432664 | | 1989 | 50.829588549102 | | 1988 | 50.829500683454 | | 1987 | 50.832700156758 | | 1986 | 50.844789914832 | | 1985 | 50.861890926654 | | 1984 | 50.879663150495 | | 1983 | 50.900616479623 | | 1982 | 50.925285558629 | | 1981 | 50.950426887375 | | 1980 | 50.974834917146 | | 1979 | 50.998313919082 | | 1978 | 51.020048325138 | | 1977 | 51.040463419576 | | 1976 | 51.062312233145 | | 1975 | 51.093840184596 | | 1974 | 51.118281976787 | | 1973 | 51.123733461991 | | 1972 | 51.126030731284 | | 1971 | 51.127508465287 | | 1970 | 51.127634520798 | | 1969 | 51.127550363887 | | 1968 | 51.127547432999 | | 1967 | 51.128682654997 | | 1966 | 51.131991568642 | | 1965 | 51.043876324018 | | 1964 | 50.855247994946 | | 1963 | 50.682374655279 | | 1962 | 50.555752717294 | | 1961 | 50.450769609595 | | 1960 | 50.431851625553 |
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