| Year | Value | | 2022 | 1.135854588928 | | 2021 | 1.2300978874164 | | 2020 | 1.3233844648436 | | 2019 | 1.2358113525582 | | 2018 | 1.3499821926568 | | 2017 | 1.4849771849635 | | 2016 | 1.4693746134551 | | 2015 | 1.3681310242704 | | 2014 | 1.4337597982058 | | 2013 | 1.3407258743985 | | 2012 | 1.243702170464 | | 2011 | 1.3508555671789 | | 2010 | 1.3710351369175 | | 2009 | 1.4427423892552 | | 2008 | 1.5999716527682 | | 2007 | 1.5473938885621 | | 2006 | 1.7491098626311 | | 2005 | 1.9291613759865 | | 2004 | 1.7932923984117 | | 2003 | 1.5922511011883 | | 2002 | 1.4476499803549 | | 2001 | 1.0983343843727 | | 2000 | 0.96215031832364 | | 1999 | 0.94736957513244 | | 1998 | 0.92705546045306 | | 1997 | 0.88070784598218 | | 1996 | 0.9007163145356 | | 1995 | 0.94148511463442 | | 1994 | 0.97331539635371 | | 1993 | 1.0505525538842 | | 1992 | 1.0746897682042 | | 1991 | 1.0966096485034 | | 1990 | 1.0771544055078 | | 1989 | 1.1065431448767 | | 1988 | 1.0837906015135 | | 1987 | 1.159182011775 | | 1986 | 1.1828506836043 | | 1985 | 1.1958271620838 | | 1984 | 1.2206143691292 | | 1983 | 1.2529249726015 | | 1982 | 1.0894539821867 | | 1981 | 0.99205331966163 | | 1980 | 1.0320757141022 | | 1979 | 0.91120572356582 | | 1978 | 0.85846425250912 | | 1977 | 0.89214308872798 | | 1976 | 0.85626117552056 | | 1975 | 0.68217282496688 | | 1974 | 0.60723646141802 | | 1973 | 0.65768099398516 | | 1972 | 0.64755629855443 | | 1971 | 0.6179106023722 | | 1970 | 0.59301931548628 |
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