| Year | Value | | 2022 | 3.135 | | 2021 | 3.638 | | 2020 | 3.856 | | 2019 | 3.136 | | 2018 | 3.384 | | 2017 | 3.746 | | 2016 | 4.122 | | 2015 | 4.624 | | 2014 | 4.981 | | 2013 | 5.231 | | 2012 | 5.379 | | 2011 | 5.825 | | 2010 | 6.967 | | 2009 | 7.742 | | 2008 | 7.525 | | 2007 | 8.658 | | 2006 | 10.25 | | 2005 | 11.167 | | 2004 | 10.727 | | 2003 | 9.779 | | 2002 | 8.482 | | 2001 | 7.89 | | 2000 | 7.917 | | 1999 | 8.854 | | 1998 | 9.787 | | 1997 | 9.861 | | 1996 | 8.822 | | 1995 | 8.158 | | 1994 | 8.727 | | 1993 | 7.675 | | 1992 | 6.323 | | 1991 | 5.316 | | 1990 | 4.89 | | 1989 | 5.705 | | 1988 | 6.319 | | 1987 | 6.813 | | 1986 | 6.608 | | 1985 | 6.875 | | 1984 | 6.673 | | 1983 | 6.449 |
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