| Year | Value | | 2021 | 0.772 | | 2020 | 0.883 | | 2019 | 1.064 | | 2018 | 1.08 | | 2017 | 1.128 | | 2016 | 1.205 | | 2015 | 1.196 | | 2014 | 1.235 | | 2013 | 1.125 | | 2012 | 1.285 | | 2011 | 1.204 | | 2010 | 1.127 | | 2009 | 1.055 | | 2008 | 1.064 | | 2007 | 1.028 | | 2006 | 0.984 | | 2005 | 0.959 | | 2004 | 0.922 | | 2003 | 0.901 | | 2002 | 0.941 | | 2001 | 0.931 | | 2000 | 1.032 | | 1999 | 0.981 | | 1998 | 1.016 | | 1997 | 1.127 | | 1996 | 1.191 | | 1995 | 1.295 | | 1994 | 1.355 | | 1993 | 1.342 | | 1992 | 1.347 | | 1991 | 1.281 | | 1990 | 1.272 | | 1989 | 1.296 | | 1988 | 1.4 | | 1987 | 1.311 | | 1986 | 1.367 | | 1985 | 1.491 | | 1984 | 1.559 | | 1983 | 1.722 | | 1982 | 1.86 | | 1981 | 1.933 | | 1980 | 2.047 | | 1979 | 2.12 | | 1978 | 2.272 | | 1977 | 2.376 | | 1976 | 2.48 | | 1975 | 2.666 | | 1974 | 2.967 | | 1973 | 3.177 | | 1972 | 3.315 | | 1971 | 3.459 | | 1970 | 3.485 | | 1969 | 3.716 | | 1968 | 3.76 | | 1967 | 4.043 | | 1966 | 4.459 | | 1965 | 4.92 | | 1964 | 5.012 | | 1963 | 5.089 | | 1962 | 5.145 | | 1961 | 5.168 | | 1960 | 5.067 |
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