| Year | Value | | 2022 | 1.4499563609619 | | 2021 | 1.5120385599415 | | 2020 | 1.4721817424794 | | 2019 | 1.1967736740391 | | 2018 | 1.2345519152012 | | 2017 | 1.2488952430465 | | 2016 | 1.2405067912955 | | 2015 | 1.21369473342 | | 2014 | 1.1027387515561 | | 2013 | 1.0548852848101 | | 2012 | 1.0422496278971 | | 2011 | 1.094931042826 | | 2010 | 1.2167926817885 | | 2009 | 1.3269023986766 | | 2008 | 1.3064971751412 | | 2007 | 1.3656783468104 | | 2006 | 1.6439104314582 | | 2005 | 1.7430555555556 | | 2004 | 1.9734660033167 | | 2003 | 2.4471299093656 | | 2002 | 3.0489335006274 | | 2001 | 3.3962264150943 | | 2000 | 3.5355029585799 | | 1999 | 4.4481054365733 | | 1998 | 4.3776472815941 | | 1997 | 4.1735256126054 | | 1996 | 5.3285561163521 | | 1995 | 0.60780287474333 | | 1994 | 3.437876960193 | | 1993 | 4.536375400889 | | 1992 | 4.2906021237811 | | 1991 | 5.5091722034182 | | 1990 | 3.7291659837121 | | 1989 | 1.7537588055935 | | 1988 | 1.5942606616182 | | 1987 | 1.6752336448598 | | 1986 | 1.7955346650999 | | 1985 | 1.5883707541739 | | 1984 | 1.6040226272784 | | 1983 | 1.8951442646024 | | 1982 | 2.0030557677617 | | 1981 | 2.0391517128874 | | 1980 | 1.8768518518518 | | 1979 | 1.7474332648871 | | 1978 | 1.5881627620222 | | 1977 | 2.1522346368715 | | 1976 | 1.6138933764136 | | 1975 | 1.6287878787879 | | 1974 | 1.4715447154471 | | 1973 | 1.8848920863309 |
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