| Year | Value | | 2024 | 8.711 | | 2023 | 9.354 | | 2022 | 10.432 | | 2021 | 11.979 | | 2020 | 13.155 | | 2019 | 13.731 | | 2018 | 10.958 | | 2017 | 10.916 | | 2016 | 10.905 | | 2015 | 10.302 | | 2014 | 9.912 | | 2013 | 9.717 | | 2012 | 9.21 | | 2011 | 9.784 | | 2010 | 11.881 | | 2009 | 14.024 | | 2008 | 10.97 | | 2007 | 10.281 | | 2006 | 10.233 | | 2005 | 10.634 | | 2004 | 10.831 | | 2003 | 10.546 | | 2002 | 10.345 | | 2001 | 8.373 | | 2000 | 6.488 | | 1999 | 7.445 | | 1998 | 6.552 | | 1997 | 6.452 | | 1996 | 6.265 | | 1995 | 7.241 | | 1994 | 8.149 | | 1993 | 8.255 | | 1992 | 8.184 | | 1991 | 8.113 | | 1990 | 8.355 | | 1989 | 8.26 | | 1988 | 8.04 | | 1985 | 11.21 | | 1984 | 11.92 | | 1983 | 12.06 | | 1982 | 10.93 |
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