| Year | Value | | 2022 | 33.896182073082 | | 2021 | 33.570244246727 | | 2020 | 31.789122493805 | | 2019 | 32.046076536022 | | 2018 | 32.793629772329 | | 2017 | 32.628361911821 | | 2016 | 32.041722279012 | | 2015 | 32.692829765405 | | 2014 | 33.953255212721 | | 2013 | 34.080100323255 | | 2012 | 35.152254107826 | | 2011 | 35.860475016181 | | 2010 | 36.543779682226 | | 2009 | 35.253653357597 | | 2008 | 37.568585881239 | | 2007 | 36.991628116763 | | 2006 | 36.112249464939 | | 2005 | 34.298514445907 | | 2004 | 33.752142286201 | | 2003 | 31.594002573139 | | 2002 | 29.934347386073 | | 2001 | 29.050490832611 | | 2000 | 28.816501061536 | | 1999 | 28.076344750852 | | 1998 | 28.642664206683 | | 1997 | 29.445967442832 | | 1996 | 29.449410766148 | | 1995 | 29.866632341941 | | 1994 | 31.423874311348 | | 1993 | 31.412383814512 | | 1992 | 30.334179833776 | | 1991 | 29.187007434937 | | 1990 | 28.366972704222 | | 1989 | 29.590105896831 | | 1988 | 30.10194630348 | | 1987 | 29.046250589425 | | 1986 | 27.548881794248 | | 1985 | 28.511125570841 | | 1984 | 27.526396001426 | | 1983 | 26.695889277943 | | 1982 | 26.759880737946 |
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