| Year | Value | | 2022 | 3.6869035600878 | | 2021 | 2.6215839566339 | | 2020 | 3.3001773547097 | | 2019 | 3.8795367601269 | | 2018 | 1.8273937977233 | | 2017 | 0.10077574877604 | | 2016 | -1.2624196887222 | | 2015 | -4.4157437212521 | | 2014 | -6.852117676077 | | 2013 | -5.0338101599168 | | 2012 | 0.55212397276583 | | 2011 | 1.7448184623813 | | 2010 | 2.3111886085126 | | 2009 | 1.6312166248993 | | 2008 | 3.6566789699347 | | 2007 | 6.3357203964112 | | 2006 | 4.4644497379198 | | 2005 | 2.724920095934 | | 2004 | 2.6484035267574 | | 2003 | 2.5728530627656 | | 2002 | 2.5734537058554 | | 2001 | 2.5446285409891 | | 2000 | 2.5239927186326 | | 1999 | 2.5519649909008 | | 1998 | 2.5915646483178 | | 1997 | 2.6508019525265 | | 1996 | 2.7251670389786 | | 1995 | 2.7684368118055 | | 1994 | 2.8084177049001 | | 1993 | 2.8522321195954 | | 1992 | 2.884887326804 | | 1991 | 2.9638221580754 | | 1990 | 3.0677656184809 | | 1989 | 3.1770955214314 | | 1988 | 3.2843702494086 | | 1987 | 3.3667843672059 | | 1986 | 3.419614083888 | | 1985 | 3.4532179945469 | | 1984 | 3.4738890942345 | | 1983 | 3.3571165776176 | | 1982 | 3.2824643661849 | | 1981 | 3.3664772974521 | | 1980 | 3.4084681788813 | | 1979 | 3.4363338309284 | | 1978 | 3.4386751516294 | | 1977 | 3.4287655709408 | | 1976 | 3.4291567315057 | | 1975 | 3.4221836019372 | | 1974 | 3.3943003804444 | | 1973 | 3.4068909954213 | | 1972 | 3.4574239520643 | | 1971 | 3.4119298183531 | | 1970 | 3.3442470761951 | | 1969 | 3.3044872064956 | | 1968 | 3.2558506335098 | | 1967 | 3.2190622696713 | | 1966 | 3.1816575227819 | | 1965 | 3.1333628972184 | | 1964 | 3.0759568001431 | | 1963 | 3.0232961028536 | | 1962 | 2.9745741252798 | | 1961 | 3.0085221341161 |
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