| Year | Value | | 2024 | 30.106061809106 | | 2023 | 31.780396402646 | | 2022 | 33.994492711729 | | 2021 | 33.715143131599 | | 2020 | 30.098808581994 | | 2019 | 29.572948542309 | | 2018 | 30.665748997679 | | 2017 | 28.789167136662 | | 2016 | 27.347782180912 | | 2015 | 27.792133369512 | | 2014 | 26.830012566228 | | 2013 | 26.339937082162 | | 2012 | 25.445175992148 | | 2011 | 24.632235134282 | | 2010 | 24.043942060921 | | 2009 | 23.357563501902 | | 2008 | 26.109114069905 | | 2007 | 25.283078083542 | | 2006 | 25.817966823658 | | 2005 | 24.725846755137 | | 2004 | 22.788002023427 | | 2003 | 21.439423805006 | | 2002 | 23.072736594007 | | 2001 | 23.26812613017 | | 2000 | 21.780821792671 | | 1999 | 22.023540195725 | | 1998 | 27.144764826084 | | 1997 | 27.712543449272 | | 1996 | 29.022005524642 | | 1995 | 28.567197838652 | | 1994 | 18.191319313568 | | 1993 | 18.513951818464 | | 1992 | 18.348793818733 | | 1991 | 18.552669829995 | | 1990 | 21.691362290051 | | 1989 | 26.076821222933 | | 1988 | 28.425803930369 | | 1987 | 24.171653825719 | | 1986 | 38.402916641379 | | 1985 | 34.822732259122 | | 1984 | 29.402416682199 | | 1983 | 28.805822031095 | | 1982 | 31.864356379024 | | 1981 | 32.51284647513 | | 1980 | 28.824322257485 | | 1979 | 33.705698139016 | | 1978 | 30.930653012201 | | 1977 | 31.930985515479 | | 1976 | 34.099125364432 |
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