| Year | Value | | 2022 | 1.3900550095965 | | 2021 | 1.326785590338 | | 2020 | 1.3735857145794 | | 2019 | 1.2621502565313 | | 2018 | 1.1705485447711 | | 2017 | 1.1534037206626 | | 2016 | 1.1512303731729 | | 2015 | 1.1373384266633 | | 2014 | 1.1499419969051 | | 2013 | 1.1852579010084 | | 2012 | 1.2416774790461 | | 2011 | 1.2061503363578 | | 2010 | 1.2668266261114 | | 2009 | 1.3106040732215 | | 2008 | 1.2090340036678 | | 2007 | 1.1724717649177 | | 2006 | 1.1993029583913 | | 2005 | 1.0656297005213 | | 2004 | 1.268957396404 | | 2003 | 1.3169248650283 | | 2002 | 1.3279581209234 | | 2001 | 1.3234383027941 | | 2000 | 1.358883033179 | | 1999 | 1.3950743545643 | | 1998 | 1.3908947861665 | | 1997 | 1.4093017326479 | | 1996 | 1.4658584599439 | | 1995 | 1.4950220142765 | | 1994 | 1.5502764327539 | | 1993 | 1.6935383226344 | | 1992 | 1.8604799411358 | | 1991 | 1.9978349881888 | | 1990 | 2.5184327066083 | | 1989 | 2.5324305336368 | | 1988 | 2.6409099301182 | | 1987 | 2.7722990262981 | | 1986 | 2.7903285669851 | | 1985 | 2.8673794844547 | | 1984 | 2.9262246615906 | | 1983 | 3.0269739405214 | | 1982 | 3.0342956295 | | 1981 | 3.0418796886871 | | 1980 | 2.9613497596583 | | 1979 | 2.9641823832573 | | 1978 | 3.0494445520826 | | 1977 | 3.038293711313 | | 1976 | 3.1355665940908 | | 1975 | 3.2832161608146 | | 1974 | 3.2611413303771 | | 1973 | 3.1596173330664 | | 1972 | 3.1675075661233 | | 1971 | 3.0602135619166 | | 1970 | 3.0126306441914 | | 1969 | 3.3986228937299 | | 1968 | 3.4063872899672 | | 1967 | 4.0776762935123 | | 1966 | 3.9092968375278 | | 1965 | 4.0910724505899 | | 1964 | 4.3842997195476 | | 1963 | 4.8992839748569 | | 1962 | 4.4959672202833 | | 1961 | 3.7399062756665 | | 1960 | 3.7698628621708 |
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