| Year | Value | | 2022 | 21.702803592845 | | 2021 | 19.658593470264 | | 2020 | 21.819265171633 | | 2019 | 22.684917151454 | | 2018 | 21.327637397102 | | 2017 | 23.598133814705 | | 2016 | 24.194627258837 | | 2015 | 16.57924219555 | | 2014 | 25.139910734988 | | 2013 | 22.470990179026 | | 2012 | 18.542175879177 | | 2011 | 16.587991711568 | | 2010 | 18.691305803841 | | 2009 | 17.699545097147 | | 2008 | 22.376132120662 | | 2007 | 16.804894776556 | | 2006 | 17.520913267777 | | 2005 | 20.843931499278 | | 2004 | 20.945562042319 | | 2003 | 17.803974397912 | | 2002 | 16.615832673895 | | 2001 | 14.563667336754 | | 2000 | 14.356493038459 | | 1999 | 17.582313822561 | | 1998 | 18.861356929758 | | 1997 | 24.229722482409 | | 1996 | 21.83430166631 | | 1995 | 15.033501818098 | | 1994 | 18.864202247589 | | 1993 | 16.011672108044 | | 1992 | 13.086161191846 | | 1991 | 7.3862052332815 | | 1990 | 4.5410719580708 | | 1989 | 5.592125240478 | | 1988 | 4.2830631290357 | | 1987 | 3.0800743941203 | | 1986 | 5.1214869080619 | | 1985 | 5.6623254244498 | | 1984 | 7.3645604987662 | | 1983 | 5.0052075583991 | | 1982 | 3.6739380022962 |
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