| Year | Value | | 2022 | 50.577032053071 | | 2021 | 50.592111754335 | | 2020 | 50.610660308537 | | 2019 | 50.622741672778 | | 2018 | 50.629861782944 | | 2017 | 50.658662784986 | | 2016 | 50.712619776823 | | 2015 | 50.781972639727 | | 2014 | 50.830006333619 | | 2013 | 50.846060259949 | | 2012 | 50.857119921621 | | 2011 | 50.854436476915 | | 2010 | 50.840603125741 | | 2009 | 50.787299302722 | | 2008 | 50.722534669451 | | 2007 | 50.690749513316 | | 2006 | 50.667848362307 | | 2005 | 50.644091501656 | | 2004 | 50.618962615533 | | 2003 | 50.590830032894 | | 2002 | 50.56879619204 | | 2001 | 50.553546348528 | | 2000 | 50.554331014449 | | 1999 | 50.57181583206 | | 1998 | 50.572050362255 | | 1997 | 50.570977409253 | | 1996 | 50.502276230942 | | 1995 | 50.408279483382 | | 1994 | 50.452912484265 | | 1993 | 50.573358398711 | | 1992 | 50.614343938699 | | 1991 | 50.580080864512 | | 1990 | 50.547897177182 | | 1989 | 50.516446055616 | | 1988 | 50.444122714296 | | 1987 | 50.449079365619 | | 1986 | 50.526383033638 | | 1985 | 50.597327159844 | | 1984 | 50.62214807622 | | 1983 | 50.623264200263 | | 1982 | 50.621436510832 | | 1981 | 50.535042856216 | | 1980 | 50.44286459824 | | 1979 | 50.388097827029 | | 1978 | 50.383382084242 | | 1977 | 50.394757791158 | | 1976 | 50.413972535885 | | 1975 | 50.436227277982 | | 1974 | 50.459055257389 | | 1973 | 50.48209727058 | | 1972 | 50.510592195687 | | 1971 | 50.539950488986 | | 1970 | 50.564215866541 | | 1969 | 50.588937453551 | | 1968 | 50.616316449849 | | 1967 | 50.638945185621 | | 1966 | 50.657306350929 | | 1965 | 50.679212419167 | | 1964 | 50.705847067856 | | 1963 | 50.734574063283 | | 1962 | 50.762995623518 | | 1961 | 50.794480228124 | | 1960 | 50.826142364748 |
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