| Year | Value | | 2022 | 49.61154060599 | | 2021 | 49.638966308834 | | 2020 | 49.626351474394 | | 2019 | 49.572037930495 | | 2018 | 49.482087643525 | | 2017 | 49.388130867907 | | 2016 | 49.287279742045 | | 2015 | 49.178172313076 | | 2014 | 49.061921278306 | | 2013 | 48.937110073244 | | 2012 | 48.802098891172 | | 2011 | 48.659499842135 | | 2010 | 48.50952796567 | | 2009 | 48.34411984444 | | 2008 | 48.176204501454 | | 2007 | 48.101121024937 | | 2006 | 48.113126139543 | | 2005 | 48.121162138511 | | 2004 | 48.124913207802 | | 2003 | 48.133117113101 | | 2002 | 48.150900877324 | | 2001 | 48.172645180124 | | 2000 | 48.187474769431 | | 1999 | 48.201537751505 | | 1998 | 48.221274665277 | | 1997 | 48.334870913888 | | 1996 | 48.427926831398 | | 1995 | 48.403530720773 | | 1994 | 48.409257478739 | | 1993 | 48.409409607835 | | 1992 | 48.358617111542 | | 1991 | 48.286186990847 | | 1990 | 48.203009094731 | | 1989 | 48.125072643447 | | 1988 | 48.031554540717 | | 1987 | 47.9194484024 | | 1986 | 47.816613024721 | | 1985 | 47.692198177677 | | 1984 | 47.592879405525 | | 1983 | 47.541818902983 | | 1982 | 47.491878651848 | | 1981 | 47.499553723568 | | 1980 | 47.50987363089 | | 1979 | 47.460416411238 | | 1978 | 47.407164123691 | | 1977 | 47.358793940199 | | 1976 | 47.357823761031 | | 1975 | 47.407341988283 | | 1974 | 47.474647408941 | | 1973 | 47.555277239176 | | 1972 | 47.646905320077 | | 1971 | 47.74803094218 | | 1970 | 47.854538064647 | | 1969 | 47.96344635414 | | 1968 | 48.071831444931 | | 1967 | 48.160571040773 | | 1966 | 48.195486648231 | | 1965 | 48.196447747588 | | 1964 | 48.209525771997 | | 1963 | 48.243024190384 | | 1962 | 48.29091311934 | | 1961 | 48.342498392219 | | 1960 | 48.390882877139 |
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