| Year | Value | | 2022 | 50.682809416882 | | 2021 | 50.694808765607 | | 2020 | 50.709395731989 | | 2019 | 50.723413877078 | | 2018 | 50.737849681345 | | 2017 | 50.751480993656 | | 2016 | 50.766013890629 | | 2015 | 50.782640401429 | | 2014 | 50.795227642288 | | 2013 | 50.803331922402 | | 2012 | 50.813067104692 | | 2011 | 50.823430946059 | | 2010 | 50.833831249726 | | 2009 | 50.846187018838 | | 2008 | 50.861251960662 | | 2007 | 50.875065529718 | | 2006 | 50.886159996291 | | 2005 | 50.894711031798 | | 2004 | 50.899978584809 | | 2003 | 50.90280420167 | | 2002 | 50.904350105329 | | 2001 | 50.905533628652 | | 2000 | 50.905088586233 | | 1999 | 50.903653106036 | | 1998 | 50.902002416207 | | 1997 | 50.898588108558 | | 1996 | 50.894153515963 | | 1995 | 50.890156488611 | | 1994 | 50.885230508422 | | 1993 | 50.879708027309 | | 1992 | 50.876665076355 | | 1991 | 50.876493590159 | | 1990 | 50.877952224215 | | 1989 | 50.880493998125 | | 1988 | 50.886394560808 | | 1987 | 50.893764315747 | | 1986 | 50.90032183467 | | 1985 | 50.906384758913 | | 1984 | 50.911950318966 | | 1983 | 50.917838530976 | | 1982 | 50.923942573825 | | 1981 | 50.924049362633 | | 1980 | 50.918964708721 | | 1979 | 50.923274850828 | | 1978 | 50.934016634618 | | 1977 | 50.939890257197 | | 1976 | 50.943146723354 | | 1975 | 50.946149516466 | | 1974 | 50.942299369555 | | 1973 | 50.931387971992 | | 1972 | 50.920110376389 | | 1971 | 50.922269865003 | | 1970 | 50.927961879019 | | 1969 | 50.923706888938 | | 1968 | 50.919665314899 | | 1967 | 50.915353353818 | | 1966 | 50.910171697732 | | 1965 | 50.902305085981 | | 1964 | 50.892211730076 | | 1963 | 50.881595538853 | | 1962 | 50.870840126297 | | 1961 | 50.860992724084 | | 1960 | 50.851805801968 |
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