| Year | Value | | 2022 | 50.766946665949 | | 2021 | 50.760744868336 | | 2020 | 50.748902435275 | | 2019 | 50.748336612161 | | 2018 | 50.757583776074 | | 2017 | 50.769258613883 | | 2016 | 50.782622289579 | | 2015 | 50.798570920392 | | 2014 | 50.81569064263 | | 2013 | 50.832286770909 | | 2012 | 50.850200422823 | | 2011 | 50.869178121162 | | 2010 | 50.879762266779 | | 2009 | 50.880773217224 | | 2008 | 50.882339236289 | | 2007 | 50.885844074269 | | 2006 | 50.889277154078 | | 2005 | 50.893620844819 | | 2004 | 50.898817555591 | | 2003 | 50.902712308543 | | 2002 | 50.903577114105 | | 2001 | 50.903505345571 | | 2000 | 50.907358633101 | | 1999 | 50.914302950773 | | 1998 | 50.919149041381 | | 1997 | 50.922352102727 | | 1996 | 50.925196562792 | | 1995 | 50.928017797032 | | 1994 | 50.93162306916 | | 1993 | 50.936344919408 | | 1992 | 50.941897236825 | | 1991 | 50.948794458943 | | 1990 | 50.957005915271 | | 1989 | 50.965334682189 | | 1988 | 50.972038511041 | | 1987 | 50.97745856481 | | 1986 | 50.98347627115 | | 1985 | 50.989047374267 | | 1984 | 50.992208486744 | | 1983 | 50.994220231719 | | 1982 | 50.995388648281 | | 1981 | 50.994480794654 | | 1980 | 50.994073018868 | | 1979 | 50.989301332202 | | 1978 | 50.97715618831 | | 1977 | 50.96471948556 | | 1976 | 50.952490209564 | | 1975 | 50.946197012078 | | 1974 | 50.951240892212 | | 1973 | 50.960407693034 | | 1972 | 50.971516433482 | | 1971 | 50.989118422828 | | 1970 | 51.010966154165 | | 1969 | 51.024459639252 | | 1968 | 51.02529766787 | | 1967 | 51.016306319566 | | 1966 | 51.000999280648 | | 1965 | 50.989679602628 | | 1964 | 50.990164321992 | | 1963 | 50.997102237821 | | 1962 | 51.003773892222 | | 1961 | 51.009758039656 | | 1960 | 51.017118810393 |
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