| Year | Value | | 2021 | 0.907 | | 2020 | 0.922 | | 2019 | 0.982 | | 2018 | 1.035 | | 2017 | 1.101 | | 2016 | 1.2425 | | 2015 | 1.3365 | | 2014 | 1.432 | | 2013 | 1.47 | | 2012 | 1.5425 | | 2011 | 1.5965 | | 2010 | 1.6235 | | 2009 | 1.6528 | | 2008 | 1.6516 | | 2007 | 1.6505 | | 2006 | 1.7123 | | 2005 | 1.7702 | | 2004 | 1.7822 | | 2003 | 1.7624 | | 2002 | 1.8317 | | 2001 | 1.9346 | | 2000 | 2.0485 | | 1999 | 2 | | 1998 | 1.9 | | 1997 | 1.9 | | 1996 | 1.94 | | 1995 | 2.248 | | 1994 | 2.278 | | 1993 | 2.307 | | 1992 | 2.29 | | 1991 | 2.302 | | 1990 | 2.378 | | 1989 | 2.386 | | 1988 | 2.307 | | 1987 | 2.328 | | 1986 | 2.355 | | 1985 | 2.351 | | 1984 | 2.353 | | 1983 | 2.456 | | 1982 | 2.613 | | 1981 | 2.711 | | 1980 | 2.815 | | 1979 | 2.846 | | 1978 | 2.9 | | 1977 | 2.923 | | 1976 | 2.863 | | 1975 | 2.772 | | 1974 | 2.882 | | 1973 | 2.93 | | 1972 | 3.058 | | 1971 | 3.291 | | 1970 | 3.243 | | 1969 | 3.315 | | 1968 | 3.381 | | 1967 | 3.569 | | 1966 | 3.817 | | 1965 | 4.044 | | 1964 | 4.108 | | 1963 | 4.525 | | 1962 | 4.359 | | 1961 | 4.51 | | 1960 | 4.796 |
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