| Year | Value | | 2021 | 1.610541727672 | | 2020 | 1.610541727672 | | 2019 | 1.610541727672 | | 2018 | 1.610541727672 | | 2017 | 1.610541727672 | | 2016 | 1.610541727672 | | 2015 | 1.610541727672 | | 2014 | 1.610541727672 | | 2013 | 1.610541727672 | | 2012 | 1.5519765739385 | | 2011 | 1.5519765739385 | | 2010 | 1.493411420205 | | 2009 | 1.4641288433382 | | 2008 | 1.4348462664715 | | 2007 | 1.4348462664715 | | 2006 | 1.4348462664715 | | 2005 | 1.4348462664715 | | 2004 | 1.4348462664715 | | 2003 | 1.4348462664715 | | 2002 | 1.4348462664715 | | 2001 | 1.4348462664715 | | 2000 | 1.4348462664715 | | 1999 | 1.4494875549048 | | 1998 | 1.4377745241581 | | 1997 | 1.4348462664715 | | 1996 | 1.3967789165447 | | 1995 | 1.3909224011713 | | 1994 | 1.385065885798 | | 1993 | 1.4202049780381 | | 1992 | 1.4055636896047 | | 1991 | 1.4084919472914 | | 1990 | 1.402635431918 | | 1989 | 1.4699853587116 | | 1988 | 1.4641288433382 | | 1987 | 1.4582723279649 | | 1986 | 1.5373352855051 | | 1985 | 1.5461200585652 | | 1984 | 1.5285505124451 | | 1983 | 1.5226939970717 | | 1982 | 1.510980966325 | | 1981 | 1.4377745241581 | | 1980 | 1.4289897510981 | | 1979 | 1.4202049780381 | | 1978 | 1.4143484626647 | | 1977 | 1.5461200585652 | | 1976 | 1.5549048316252 | | 1975 | 1.5431918008785 | | 1974 | 1.5402635431918 | | 1973 | 1.5344070278185 | | 1972 | 1.5226939970717 | | 1971 | 1.5226939970717 | | 1970 | 1.5226939970717 | | 1969 | 1.5197657393851 | | 1968 | 1.5168374816984 | | 1967 | 1.5168374816984 | | 1966 | 1.5168374816984 | | 1965 | 1.5168374816984 | | 1964 | 1.5168374816984 | | 1963 | 1.5226939970717 | | 1962 | 1.5226939970717 | | 1961 | 1.5226939970717 |
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