| Year | Value | | 2021 | 0.808 | | 2020 | 0.837 | | 2019 | 0.918 | | 2018 | 0.977 | | 2017 | 1.052 | | 2016 | 1.172 | | 2015 | 1.239 | | 2014 | 1.205 | | 2013 | 1.187 | | 2012 | 1.297 | | 2011 | 1.244 | | 2010 | 1.226 | | 2009 | 1.149 | | 2008 | 1.192 | | 2007 | 1.259 | | 2006 | 1.132 | | 2005 | 1.085 | | 2004 | 1.164 | | 2003 | 1.191 | | 2002 | 1.178 | | 2001 | 1.309 | | 2000 | 1.48 | | 1999 | 1.425 | | 1998 | 1.464 | | 1997 | 1.537 | | 1996 | 1.574 | | 1995 | 1.634 | | 1994 | 1.656 | | 1993 | 1.654 | | 1992 | 1.76 | | 1991 | 1.71 | | 1990 | 1.57 | | 1989 | 1.56 | | 1988 | 1.55 | | 1987 | 1.53 | | 1986 | 1.58 | | 1985 | 1.66 | | 1984 | 1.74 | | 1983 | 2.06 | | 1982 | 2.39 | | 1981 | 2.57 | | 1980 | 2.82 | | 1979 | 2.9 | | 1978 | 2.64 | | 1977 | 2.99 | | 1976 | 3 | | 1975 | 3.43 | | 1974 | 3.77 | | 1973 | 4.07 | | 1972 | 4.12 | | 1971 | 4.54 | | 1970 | 4.53 | | 1969 | 4.47 | | 1968 | 4.489 | | 1967 | 4.634 | | 1966 | 4.81 | | 1965 | 4.995 | | 1964 | 5.188 | | 1963 | 5.407 | | 1962 | 5.624 | | 1961 | 5.81 | | 1960 | 5.949 |
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