| Year | Value | | 2022 | 48.763730982122 | | 2021 | 48.739190830625 | | 2020 | 48.718712468327 | | 2019 | 48.704612776481 | | 2018 | 48.672781102394 | | 2017 | 48.610075069622 | | 2016 | 48.548147124986 | | 2015 | 48.496441463409 | | 2014 | 48.462789130563 | | 2013 | 48.440275306325 | | 2012 | 48.410406720236 | | 2011 | 48.393161677802 | | 2010 | 48.403465588588 | | 2009 | 48.420594981358 | | 2008 | 48.431597960213 | | 2007 | 48.442892757931 | | 2006 | 48.451773058737 | | 2005 | 48.449525906206 | | 2004 | 48.430938250083 | | 2003 | 48.404446307739 | | 2002 | 48.38568619362 | | 2001 | 48.379553270583 | | 2000 | 48.382949337659 | | 1999 | 48.391286493854 | | 1998 | 48.404188375232 | | 1997 | 48.417529485752 | | 1996 | 48.430000660996 | | 1995 | 48.44418029416 | | 1994 | 48.459889797483 | | 1993 | 48.474105272753 | | 1992 | 48.48574472819 | | 1991 | 48.498823539023 | | 1990 | 48.511887462667 | | 1989 | 48.523372427798 | | 1988 | 48.5340568512 | | 1987 | 48.544297216342 | | 1986 | 48.554862869002 | | 1985 | 48.56539333802 | | 1984 | 48.577296690275 | | 1983 | 48.588954159374 | | 1982 | 48.600751604955 | | 1981 | 48.616605796517 | | 1980 | 48.570079163874 | | 1979 | 48.525366502613 | | 1978 | 48.548045228471 | | 1977 | 48.569367000884 | | 1976 | 48.587383082626 | | 1975 | 48.60213153199 | | 1974 | 48.613674828495 | | 1973 | 48.622322988801 | | 1972 | 48.630052377403 | | 1971 | 48.627725517473 | | 1970 | 48.613445163828 | | 1969 | 48.600414218442 | | 1968 | 48.587542942063 | | 1967 | 48.570656896961 | | 1966 | 48.553174051455 | | 1965 | 48.534368958426 | | 1964 | 48.513782248073 | | 1963 | 48.494807490152 | | 1962 | 48.478356580731 | | 1961 | 48.477501634622 | | 1960 | 48.496409577285 |
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