| Year | Value | | 2022 | 1.5832811384635 | | 2021 | 1.3766470953669 | | 2020 | 1.4412639825242 | | 2019 | 1.3183609964886 | | 2018 | 1.2166741818661 | | 2017 | 1.1568036675671 | | 2016 | 1.163626917696 | | 2015 | 1.1327115047942 | | 2014 | 1.1596878908809 | | 2013 | 1.1661516239365 | | 2012 | 1.2354088880585 | | 2011 | 1.2883653489842 | | 2010 | 1.3254337150161 | | 2009 | 1.3976333217037 | | 2008 | 1.3053192376985 | | 2007 | 1.3547167982945 | | 2006 | 1.3933890574908 | | 2005 | 1.3964852790883 | | 2004 | 1.426827839769 | | 2003 | 1.4438095980968 | | 2002 | 1.4265560116295 | | 2001 | 1.4379068691233 | | 2000 | 1.4340043406407 | | 1999 | 1.5898254258289 | | 1998 | 1.5806480613385 | | 1997 | 1.659273182614 | | 1996 | 1.756607735714 | | 1995 | 1.7942405045783 | | 1994 | 1.9130609754514 | | 1993 | 2.0278294084545 | | 1992 | 2.213002596309 | | 1991 | 2.2485315309384 | | 1990 | 2.3690198851014 | | 1989 | 2.5174039055059 | | 1988 | 2.6109094684565 | | 1987 | 2.7134671779833 | | 1986 | 2.7251197859885 | | 1985 | 2.7682181209482 | | 1984 | 2.8617244173865 | | 1983 | 2.8485847447994 | | 1982 | 3.1414705898142 | | 1981 | 2.8631194423343 | | 1980 | 2.7842985662075 | | 1979 | 2.8402328282409 | | 1978 | 2.7470705306056 | | 1977 | 2.9544575220689 | | 1976 | 2.6889094493665 | | 1975 | 2.843860128566 | | 1974 | 2.6534716614633 | | 1973 | 2.7029972496203 | | 1972 | 2.8185399996365 | | 1971 | 2.8388295348653 | | 1970 | 2.8662355543566 | | 1969 | 3.2289286032292 | | 1968 | 3.2563349201726 | | 1967 | 3.5233358058519 | | 1966 | 3.3702842854495 | | 1965 | 3.5712903313516 | | 1964 | 3.9326526841831 | | 1963 | 4.010834481973 | | 1962 | 4.122775250128 | | 1961 | 4.08728387914 | | 1960 | 3.7039017965883 |
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