| Year | Value | | 2022 | 8.3064612444762 | | 2021 | 5.706350208307 | | 2020 | 5.6341511589763 | | 2019 | 6.720075328638 | | 2018 | 7.3075917603165 | | 2017 | 5.3088483956584 | | 2016 | 3.6293993738438 | | 2015 | 4.437371273215 | | 2014 | 4.6255509953403 | | 2013 | 5.3162353132669 | | 2012 | 4.6118443220664 | | 2011 | 3.2400284200953 | | 2010 | 3.3389796360107 | | 2009 | 3.6649033064292 | | 2008 | 4.3450280762304 | | 2007 | 2.9669443247735 | | 2006 | 3.2252533743892 | | 2005 | 2.0177864135714 | | 2004 | 3.6322800495662 | | 2003 | 2.7125924747435 | | 2002 | 2.7210328485045 | | 2001 | 1.9833333333334 | | 2000 | 2.9623079473861 | | 1999 | 2.6901248581158 | | 1998 | 3.1253657965586 | | 1997 | 3.6520262072307 | | 1996 | 3.7251447269071 | | 1995 | 6.2441502874715 | | 1994 | 4.733230639966 | | 1993 | 3.9749563191613 | | 1992 | 5.8243451463791 | | 1991 | 8.1937150954409 | | 1990 | 6.5452930728241 | | 1989 | 7.7408860396134 | | 1988 | 7.1969696969695 | | 1987 | 8.2258064516129 | | 1986 | 6.1643835616437 | | 1985 | 7.2543617998164 | | 1984 | 8.9000000000001 |
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