| Year | Value | | 2022 | 1.604757742552 | | 2021 | 1.6367427551677 | | 2020 | 1.8509857638725 | | 2019 | 1.9508563479621 | | 2018 | 2.0427851007848 | | 2017 | 2.0792225136908 | | 2016 | 2.0288024896991 | | 2015 | 1.9623689120525 | | 2014 | 1.9250853676966 | | 2013 | 1.9056269699456 | | 2012 | 1.920855668993 | | 2011 | 2.0055569612499 | | 2010 | 2.060951632168 | | 2009 | 2.0549906069 | | 2008 | 2.030265265269 | | 2007 | 1.9649571637883 | | 2006 | 1.8787362307276 | | 2005 | 1.7976481258718 | | 2004 | 1.7484142933391 | | 2003 | 1.7522845551766 | | 2002 | 1.866764357359 | | 2001 | 2.0032685597646 | | 2000 | 2.0727115801598 | | 1999 | 2.1426721586194 | | 1998 | 2.219597187298 | | 1997 | 2.3230613842714 | | 1996 | 2.4657313570936 | | 1995 | 2.6314388804012 | | 1994 | 2.7840436228099 | | 1993 | 2.8838363340504 | | 1992 | 2.86395904419 | | 1991 | 2.8737588649831 | | 1990 | 3.0120185722822 | | 1989 | 3.1528088136861 | | 1988 | 3.2974018932185 | | 1987 | 3.4257049536879 | | 1986 | 3.4998893471393 | | 1985 | 3.5335424068902 | | 1984 | 3.5610254984345 | | 1983 | 3.6196809967986 | | 1982 | 4.0151851927933 | | 1981 | 4.5985747718051 | | 1980 | 4.921962932142 | | 1979 | 5.0623180555009 | | 1978 | 5.1239139596663 | | 1977 | 5.1548473041388 | | 1976 | 5.1530651678968 | | 1975 | 5.1241960520382 | | 1974 | 5.0904551579847 | | 1973 | 4.7748403195949 | | 1972 | 3.6505670522541 | | 1971 | 1.988559177806 | | 1970 | 0.93420335887473 | | 1969 | 0.69814340783132 | | 1968 | 0.6771292419241 | | 1967 | 0.67061169612551 | | 1966 | 0.67724092227334 | | 1965 | 1.5356150293905 | | 1964 | 2.3816155606839 | | 1963 | 2.3240770063625 | | 1962 | 2.2671877199037 | | 1961 | 2.2247820053062 |
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