| Year | Value | | 2021 | 33.581566465414 | | 2020 | 33.152144304751 | | 2019 | 33.44143550699 | | 2018 | 33.30552846974 | | 2017 | 33.75566099496 | | 2016 | 32.80842106952 | | 2015 | 32.997098516153 | | 2014 | 33.842043440992 | | 2013 | 33.796140868598 | | 2012 | 34.274788853124 | | 2011 | 34.643878921746 | | 2010 | 34.137061550486 | | 2009 | 34.508798645204 | | 2008 | 34.795908731209 | | 2007 | 35.143649516414 | | 2006 | 35.558552021014 | | 2005 | 35.66287058971 | | 2004 | 35.186737915032 | | 2003 | 36.624700206559 | | 2002 | 36.917184033663 | | 2001 | 37.278092685887 | | 2000 | 37.301333775976 | | 1999 | 37.306600535284 | | 1998 | 37.679516675789 | | 1997 | 37.670360066447 | | 1996 | 37.835596184366 | | 1995 | 37.916580739471 | | 1994 | 38.166006234643 | | 1993 | 37.957082224544 | | 1992 | 38.225457139114 | | 1991 | 37.460475938653 | | 1990 | 37.587565586462 | | 1989 | 37.700108612996 | | 1988 | 37.868407140041 | | 1987 | 37.848412651556 | | 1986 | 37.912204085997 | | 1985 | 38.523144183112 | | 1984 | 38.532119266104 | | 1983 | 38.457827038569 | | 1982 | 38.728349702951 | | 1981 | 38.805511108772 | | 1980 | 38.812765084909 | | 1979 | 38.75436917898 | | 1978 | 38.879959134612 | | 1977 | 38.809644195406 | | 1976 | 39.132136931961 | | 1975 | 39.092102869461 | | 1974 | 39.113216496759 | | 1973 | 39.086876111656 | | 1972 | 39.20079914641 | | 1971 | 39.216806581368 | | 1970 | 39.12912072328 | | 1969 | 39.801801593259 | | 1968 | 39.911267378389 | | 1967 | 39.137798678662 | | 1966 | 39.066612032624 | | 1965 | 39.068120932889 | | 1964 | 39.043440781281 | | 1963 | 39.020972071117 | | 1962 | 39.01030623316 | | 1961 | 39.041764030267 |
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