| Year | Value | | 2021 | 4.3586985347571 | | 2020 | 4.4118937040028 | | 2019 | 4.4595395062961 | | 2018 | 4.5000801290492 | | 2017 | 4.5454576602811 | | 2016 | 4.5991398820368 | | 2015 | 4.6422769396455 | | 2014 | 4.6837534068728 | | 2013 | 4.7328333657758 | | 2012 | 4.7864467706696 | | 2011 | 4.8331082703606 | | 2010 | 4.8697881409998 | | 2009 | 4.9069282813803 | | 2008 | 4.9347096208274 | | 2007 | 4.9512657680467 | | 2006 | 4.9758127851521 | | 2005 | 4.9950178285845 | | 2004 | 5.0346954827593 | | 2003 | 5.0718752878292 | | 2002 | 5.102346551597 | | 2001 | 5.1265702070968 | | 2000 | 5.1523409729558 | | 1999 | 5.1728282308306 | | 1998 | 5.2046664964029 | | 1997 | 5.2571091871405 | | 1996 | 5.3118716735634 | | 1995 | 5.3721850927787 | | 1994 | 5.4189796216465 | | 1993 | 5.4656969951293 | | 1992 | 5.5177041030291 | | 1991 | 5.5697256120926 | | 1990 | 5.6180198506435 | | 1989 | 5.6618775553341 | | 1988 | 5.6972145613135 | | 1987 | 5.7330902413866 | | 1986 | 5.7719539385314 | | 1985 | 5.8021074305148 | | 1984 | 5.8414192035192 | | 1983 | 5.8610881480792 | | 1982 | 5.8529740530286 | | 1981 | 5.8576979778776 | | 1980 | 5.8778873827603 | | 1979 | 5.8926930249177 | | 1978 | 5.8918895519952 | | 1977 | 5.8693693057307 | | 1976 | 5.8590505026486 | | 1975 | 5.8528085216881 | | 1974 | 5.8393157044025 | | 1973 | 5.8225518203127 | | 1972 | 5.8217216616708 | | 1971 | 5.8184807613736 | | 1970 | 5.7969531499899 | | 1969 | 5.7801113076683 | | 1968 | 5.7583611617025 | | 1967 | 5.7462226798669 | | 1966 | 5.7354714254907 | | 1965 | 5.7147680178908 | | 1964 | 5.6907538291662 | | 1963 | 5.6853875312504 | | 1962 | 5.6775680750335 | | 1961 | 5.6260962165543 | | 1960 | 5.6039335969501 |
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