| Year | Value | | 2021 | 36.919631673454 | | 2020 | 36.913981481441 | | 2019 | 36.853394077322 | | 2018 | 36.878518596133 | | 2017 | 36.876394472479 | | 2016 | 36.866335350149 | | 2015 | 36.863122765038 | | 2014 | 36.818220831599 | | 2013 | 36.86432701909 | | 2012 | 36.833035303959 | | 2011 | 36.817993134271 | | 2010 | 36.81734709748 | | 2009 | 36.704247885837 | | 2008 | 36.700815602112 | | 2007 | 36.768182302476 | | 2006 | 36.729682728691 | | 2005 | 36.700400511021 | | 2004 | 36.885560159667 | | 2003 | 36.851790690525 | | 2002 | 37.034467028519 | | 2001 | 37.006921772301 | | 2000 | 37.004444781034 | | 1999 | 37.007610280287 | | 1998 | 36.948618332944 | | 1997 | 36.905410573695 | | 1996 | 36.707766712756 | | 1995 | 36.694492951063 | | 1994 | 36.724254758959 | | 1993 | 36.64940863757 | | 1992 | 36.647065083154 | | 1991 | 40.023497531612 | | 1990 | 39.900759243215 | | 1989 | 39.747687243059 | | 1988 | 39.573441413676 | | 1987 | 39.435803644125 | | 1986 | 39.204473509468 | | 1985 | 39.062627904926 | | 1984 | 38.696216143296 | | 1983 | 38.366242962331 | | 1982 | 38.11279338208 | | 1981 | 37.84628660066 | | 1980 | 37.742636315601 | | 1979 | 37.559290626239 | | 1978 | 37.352015796107 | | 1977 | 37.086428429152 | | 1976 | 36.833742256422 | | 1975 | 36.873698245692 | | 1974 | 36.691536415299 | | 1973 | 36.477538595972 | | 1972 | 36.252429584377 | | 1971 | 36.011066231626 | | 1970 | 35.794382615273 | | 1969 | 35.596466600822 | | 1968 | 35.474791114823 | | 1967 | 35.318516098386 | | 1966 | 35.184065500368 | | 1965 | 35.033384508709 | | 1964 | 34.873349696851 | | 1963 | 34.734130067645 | | 1962 | 34.594530972764 | | 1961 | 34.455848905407 |
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