| Year | Value | | 2022 | 32.423650455186 | | 2021 | 30.927884686574 | | 2020 | 24.134043573116 | | 2019 | 25.971280896048 | | 2018 | 26.829454324495 | | 2017 | 30.796215087338 | | 2016 | 30.126279030133 | | 2015 | 31.307304400238 | | 2014 | 36.442663731462 | | 2013 | 29.922466445784 | | 2012 | 36.874336275493 | | 2011 | 38.61497237772 | | 2010 | 32.036922100478 | | 2009 | 27.424000433843 | | 2008 | 37.088528454929 | | 2007 | 44.516104072948 | | 2006 | 41.346296741459 | | 2005 | 40.436715703604 | | 2004 | 34.270372934879 | | 2003 | 35.678317526755 | | 2002 | 31.434561404554 | | 2001 | 43.393177166679 | | 2000 | 39.441437350485 | | 1999 | 39.691031004011 | | 1998 | 40.527018375815 | | 1997 | 37.491516891743 | | 1996 | 36.913228500433 | | 1995 | 29.008248974867 | | 1994 | 29.322317957084 | | 1993 | 43.739229120547 | | 1992 | 41.398507070268 | | 1991 | 44.99639367074 | | 1990 | 41.647819683238 | | 1989 | 47.479299846331 | | 1988 | 49.819059587543 | | 1987 | 38.702834609313 | | 1986 | 36.247085937281 | | 1985 | 32.428864954685 | | 1984 | 25.353030054455 | | 1983 | 28.906949227548 | | 1982 | 27.395818644965 | | 1981 | 28.848078635024 | | 1980 | 27.433145358673 | | 1979 | 29.803952435423 | | 1978 | 22.783515700384 | | 1977 | 22.23537431704 | | 1976 | 21.669242662832 | | 1975 | 20.255091742262 |
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