| Year | Value | | 2022 | 30.547895624799 | | 2021 | 30.911000610397 | | 2020 | 32.815968426733 | | 2019 | 42.187516051852 | | 2018 | 42.603109388234 | | 2017 | 41.880636457689 | | 2016 | 35.305067826704 | | 2015 | 40.088207691269 | | 2014 | 39.58967855243 | | 2013 | 37.081317413605 | | 2012 | 34.555332205752 | | 2011 | 29.516128612759 | | 2010 | 37.750483391881 | | 2009 | 37.248180616288 | | 2008 | 36.656912120874 | | 2007 | 31.058869652816 | | 2006 | 29.504252851021 | | 2005 | 30.685716546614 | | 2004 | 27.575834168127 | | 2003 | 25.126766111273 | | 2002 | 25.131483622946 | | 2001 | 18.550223498512 | | 2000 | 21.730513311967 | | 1999 | 20.471235093166 | | 1998 | 20.131929012562 | | 1997 | 19.110543974084 | | 1996 | 20.385082663977 | | 1995 | 21.007793878406 | | 1994 | 13.992043702326 | | 1993 | 16.625170707713 | | 1992 | 15.108862189082 | | 1991 | 11.71677401686 | | 1990 | 10.33419755214 | | 1989 | 13.246422622688 | | 1988 | 14.844279221715 | | 1987 | 16.807070538465 | | 1986 | 15.51951067117 | | 1985 | 18.623113392221 | | 1984 | 16.012586181503 | | 1983 | 14.505735853203 | | 1982 | 16.401240866442 | | 1981 | 16.895070429196 | | 1980 | 17.296478407626 | | 1979 | 16.469951760207 | | 1978 | 17.427140689403 | | 1977 | 17.443282986111 | | 1976 | 15.321277593647 |
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