| Year | Value | | 2022 | 0.75690488153298 | | 2021 | 0.82886347007094 | | 2020 | 0.92858317237706 | | 2019 | 0.96966216237603 | | 2018 | 1.0242299897106 | | 2017 | 1.070575924424 | | 2016 | 1.1004331332838 | | 2015 | 1.1209281681867 | | 2014 | 1.1321576929893 | | 2013 | 1.1203931698435 | | 2012 | 1.2775926333017 | | 2011 | 1.2538249265496 | | 2010 | 1.019946186598 | | 2009 | 0.97018755594858 | | 2008 | 0.9405653096614 | | 2007 | 0.91946352354975 | | 2006 | 0.91237167062561 | | 2005 | 0.92956525644094 | | 2004 | 0.96092596769164 | | 2003 | 0.97827321991992 | | 2002 | 0.98994899148091 | | 2001 | 1.0237896421748 | | 2000 | 1.0695386934505 | | 1999 | 1.139676089554 | | 1998 | 1.2394170105477 | | 1997 | 1.3418640231603 | | 1996 | 1.4574414015818 | | 1995 | 1.6376024727615 | | 1994 | 1.8318958637017 | | 1993 | 1.9644705860062 | | 1992 | 2.0624311806746 | | 1991 | 2.1430970670954 | | 1990 | 2.1996861017439 | | 1989 | 2.2984887575973 | | 1988 | 2.4398739266469 | | 1987 | 2.5571238216316 | | 1986 | 2.6323112082827 | | 1985 | 2.669513676327 | | 1984 | 2.6150608768454 | | 1983 | 2.5176835616394 | | 1982 | 2.5026979745796 | | 1981 | 2.4906171769019 | | 1980 | 2.492982345288 | | 1979 | 2.5463319866113 | | 1978 | 2.6258661392465 | | 1977 | 2.7078782447773 | | 1976 | 2.751229336921 | | 1975 | 2.7405580315371 | | 1974 | 2.6988937476925 | | 1973 | 2.6615942064474 | | 1972 | 2.630232137794 | | 1971 | 2.6324749430037 | | 1970 | 2.6549338326008 | | 1969 | 2.6838061517516 | | 1968 | 2.619849413394 | | 1967 | 2.438688436005 | | 1966 | 2.0362110148408 | | 1965 | 1.5342746775758 | | 1964 | 1.2953352070664 | | 1963 | 1.188266114199 | | 1962 | 1.0649855943907 | | 1961 | 0.97058905624535 |
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