| Year | Value | | 2022 | 48.493214270285 | | 2021 | 48.495759721214 | | 2020 | 48.505417903979 | | 2019 | 48.506181893255 | | 2018 | 48.490684349451 | | 2017 | 48.478759550392 | | 2016 | 48.47400108336 | | 2015 | 48.465335650579 | | 2014 | 48.452125373077 | | 2013 | 48.439134795383 | | 2012 | 48.419103075393 | | 2011 | 48.391490004812 | | 2010 | 48.360128778299 | | 2009 | 48.323104862186 | | 2008 | 48.28403918064 | | 2007 | 48.247507622391 | | 2006 | 48.217468989327 | | 2005 | 48.196423364099 | | 2004 | 48.183162634534 | | 2003 | 48.174358866843 | | 2002 | 48.167580168054 | | 2001 | 48.168692422768 | | 2000 | 48.182698006135 | | 1999 | 48.207766412927 | | 1998 | 48.251417407829 | | 1997 | 48.30644818118 | | 1996 | 48.364303656925 | | 1995 | 48.433119880098 | | 1994 | 48.510492993714 | | 1993 | 48.58848045093 | | 1992 | 48.660178069202 | | 1991 | 48.720495868906 | | 1990 | 48.777033360106 | | 1989 | 48.835177291432 | | 1988 | 48.890917249852 | | 1987 | 48.946040128562 | | 1986 | 49.000922166867 | | 1985 | 49.055138702418 | | 1984 | 49.106928918764 | | 1983 | 49.15590838451 | | 1982 | 49.198309790385 | | 1981 | 49.232759646138 | | 1980 | 49.265806784086 | | 1979 | 49.296205763332 | | 1978 | 49.32073357492 | | 1977 | 49.342103790608 | | 1976 | 49.360290184504 | | 1975 | 49.375356267389 | | 1974 | 49.387385188989 | | 1973 | 49.397011865783 | | 1972 | 49.405889758491 | | 1971 | 49.414579251607 | | 1970 | 49.419849818536 | | 1969 | 49.422119486865 | | 1968 | 49.423034625033 | | 1967 | 49.419666048415 | | 1966 | 49.410168543389 | | 1965 | 49.393298202854 | | 1964 | 49.368815590554 | | 1963 | 49.332986193033 | | 1962 | 49.289073238241 | | 1961 | 49.241229702527 | | 1960 | 49.190497019928 |
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