Year | Value | 2022 | 3.3 | 2021 | 3.7 | 2020 | 6 | 2019 | 3.5 | 2018 | 4 | 2017 | 3.1 | 2016 | 4.1 | 2015 | 4.4 | 2014 | 4.3 | 2013 | 4.3 | 2012 | 4.4 | 2011 | 4.8 | 2010 | 4.1 | 2009 | 6.1 | 2008 | 5.7 | 2007 | 5.9 | 2006 | 8.2 | 2005 | 8.5 | 2004 | 9.8 | 2003 | 10.5 | 2002 | 10.5 | 2001 | 11.5 | 2000 | 14.8 | 1999 | 14 | 1998 | 11.9 | 1997 | 15.1 | 1996 | 17.6 | 1995 | 15.3 | 1994 | 14.7 | 1993 | 17.4 | 1992 | 21.2 | 1991 | 24.5 | 1990 | 20.8 | 1989 | 21.5 | 1986 | 28.6 | 1981 | 44.4 |
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