| Year | Value | | 2022 | 32.051190019102 | | 2021 | 32.729943733511 | | 2020 | 35.748689404571 | | 2019 | 32.938074322553 | | 2018 | 31.815169459598 | | 2017 | 33.015270486439 | | 2016 | 29.051373579372 | | 2015 | 33.770145707763 | | 2014 | 36.328432719277 | | 2013 | 35.907527190845 | | 2012 | 38.08375699306 | | 2011 | 30.213747934397 | | 2010 | 30.298760430199 | | 2009 | 39.986244703384 | | 2008 | 38.258568160124 | | 2007 | 39.313797745203 | | 2006 | 33.919754342518 | | 2005 | 28.573900729932 | | 2004 | 28.961325004385 | | 2003 | 27.114882018238 | | 2002 | 24.194163048087 | | 2001 | 25.782206151658 | | 2000 | 22.939555856984 | | 1999 | 24.722215326314 | | 1998 | 25.080543341343 | | 1997 | 29.212474890817 | | 1996 | 26.961899686105 | | 1995 | 28.750497175983 | | 1994 | 29.870795750394 | | 1993 | 29.67252715708 | | 1992 | 28.301526250609 | | 1991 | 27.756576351192 | | 1989 | 34.198995396285 | | 1988 | 30.643713126378 | | 1987 | 31.913191592313 | | 1986 | 31.697153602579 | | 1985 | 35.581089875074 | | 1984 | 38.693516513543 | | 1983 | 34.95877761032 | | 1982 | 28.988354746477 |
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