| Year | Value | | 2022 | 1.3085801913436 | | 2021 | 1.3156150150044 | | 2020 | 1.4510521369147 | | 2019 | 1.6022897305527 | | 2018 | 1.6751229756162 | | 2017 | 1.7169487217003 | | 2016 | 1.7345600217223 | | 2015 | 1.7412354337726 | | 2014 | 1.7441157181209 | | 2013 | 1.7606135983041 | | 2012 | 1.7784489664692 | | 2011 | 1.7794345608363 | | 2010 | 1.7896720998449 | | 2009 | 1.8163634745699 | | 2008 | 1.8381638086969 | | 2007 | 1.8541491887089 | | 2006 | 1.879014135384 | | 2005 | 1.9104349610733 | | 2004 | 1.9207992219944 | | 2003 | 1.9236470184057 | | 2002 | 1.9400758674746 | | 2001 | 1.9560378239898 | | 2000 | 1.9718879127872 | | 1999 | 1.9883993241869 | | 1998 | 2.0019330721863 | | 1997 | 2.0139983592718 | | 1996 | 2.0242057560771 | | 1995 | 2.033821404226 | | 1994 | 2.0455139596654 | | 1993 | 2.058120865458 | | 1992 | 2.0702317907685 | | 1991 | 2.1033034574497 | | 1990 | 2.1216828939718 | | 1989 | 2.1370470341019 | | 1988 | 2.1783179359972 | | 1987 | 2.2126293074524 | | 1986 | 2.2455812767976 | | 1985 | 2.2782148884063 | | 1984 | 2.3117902619036 | | 1983 | 2.3262053563418 | | 1982 | 2.3268286964897 | | 1981 | 2.3285941160994 | | 1980 | 2.3353516008789 | | 1979 | 2.3552030420147 | | 1978 | 2.3936918885208 | | 1977 | 2.4491373588433 | | 1976 | 2.513626556455 | | 1975 | 2.5807492147796 | | 1974 | 2.6428039388625 | | 1973 | 2.704439626074 | | 1972 | 2.7565240846798 | | 1971 | 2.789148237455 | | 1970 | 2.8243241512171 | | 1969 | 2.8705923262321 | | 1968 | 2.917545238658 | | 1967 | 2.9627916796632 | | 1966 | 2.9995281477782 | | 1965 | 3.0284841674615 | | 1964 | 3.049988722361 | | 1963 | 3.0442480617411 | | 1962 | 3.0087275731564 | | 1961 | 2.9587514818814 |
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