Year | Value | 2021 | 35.188190898182 | 2020 | 35.085086402658 | 2019 | 35.073776331579 | 2018 | 34.964090556632 | 2017 | 34.774805224776 | 2016 | 34.879748084557 | 2015 | 34.847074125358 | 2014 | 34.846157851011 | 2013 | 34.836148804579 | 2012 | 34.746146035263 | 2011 | 34.657066371273 | 2010 | 34.572602233915 | 2009 | 34.493676728515 | 2008 | 34.414751223115 | 2007 | 34.335825717714 | 2006 | 34.245822948398 | 2005 | 34.119819071356 | 2004 | 33.801347733776 | 2003 | 33.829040893566 | 2002 | 34.441982830241 | 2001 | 34.298901504662 | 2000 | 34.286901135419 | 1999 | 34.218591341272 | 1998 | 34.138281177882 | 1997 | 34.03858580264 | 1996 | 33.86319579064 | 1995 | 33.785654943229 | 1994 | 33.555801716976 | 1993 | 33.428413181944 | 1992 | 33.075786947291 | 1991 | 33.04347826087 | 1990 | 32.728699344595 | 1989 | 32.74254592449 | 1988 | 32.5394627527 | 1987 | 32.518231330195 | 1986 | 32.496076802363 | 1985 | 32.019754453983 | 1984 | 32.047447613773 | 1983 | 31.545278316256 | 1982 | 31.511123419182 | 1981 | 31.476968522108 | 1980 | 30.981260961876 | 1979 | 30.947106064802 | 1978 | 30.452321609896 | 1977 | 30.419089818148 | 1976 | 29.923382257916 | 1975 | 29.890150466168 | 1974 | 29.394442905936 | 1973 | 28.900581556356 | 1972 | 28.865503553955 | 1971 | 28.370719099049 | 1970 | 27.967322071448 | 1969 | 27.934090279701 | 1968 | 27.715314317364 | 1967 | 27.682082525616 | 1966 | 27.647927628542 | 1965 | 27.614695836795 | 1964 | 27.580540939721 | 1963 | 27.515000461553 | 1962 | 27.639619680606 | 1961 | 27.731930213237 |
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