Year | Value | 2022 | 51.67297567944 | 2021 | 51.709044192979 | 2020 | 51.775185443415 | 2019 | 51.840104881765 | 2018 | 51.867287171637 | 2017 | 51.87844893848 | 2016 | 51.870500354185 | 2015 | 51.830175638866 | 2014 | 51.796258027181 | 2013 | 51.788515524651 | 2012 | 51.78059120678 | 2011 | 51.767493566336 | 2010 | 51.752643675012 | 2009 | 51.713646038491 | 2008 | 51.630412307945 | 2007 | 51.527775158511 | 2006 | 51.426134277971 | 2005 | 51.351341996707 | 2004 | 51.322785551088 | 2003 | 51.313341033509 | 2002 | 51.303645134108 | 2001 | 51.300927430252 | 2000 | 51.300544036818 | 1999 | 51.296991961287 | 1998 | 51.289406595951 | 1997 | 51.27314856108 | 1996 | 51.249615785517 | 1995 | 51.234966101897 | 1994 | 51.224585900355 | 1993 | 51.205212623046 | 1992 | 51.182180251475 | 1991 | 51.1578709115 | 1990 | 51.146233769569 | 1989 | 51.145570533804 | 1988 | 51.131976414323 | 1987 | 51.124005000843 | 1986 | 51.119531235803 | 1985 | 51.113653784033 | 1984 | 51.107282173469 | 1983 | 51.104505978054 | 1982 | 51.105949621031 | 1981 | 51.064529976537 | 1980 | 51.002046361773 | 1979 | 50.965026466443 | 1978 | 50.919905186928 | 1977 | 50.87062303077 | 1976 | 50.830543706198 | 1975 | 50.798092020935 | 1974 | 50.77510479623 | 1973 | 50.7676973743 | 1972 | 50.761286732968 | 1971 | 50.750439239807 | 1970 | 50.739123988017 | 1969 | 50.729508846272 | 1968 | 50.720292043914 | 1967 | 50.713612369695 | 1966 | 50.71054674858 | 1965 | 50.692100148705 | 1964 | 50.65838071775 | 1963 | 50.628059536387 | 1962 | 50.602014222829 | 1961 | 50.577319326855 | 1960 | 50.562387478281 |
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