| Year | Value | | 2022 | 14.416769352323 | | 2021 | 14.147036771817 | | 2020 | 13.959059140115 | | 2019 | 14.166091539941 | | 2018 | 14.015602945173 | | 2017 | 13.864424400687 | | 2016 | 13.671048772775 | | 2015 | 13.528507102505 | | 2014 | 13.400540284185 | | 2013 | 13.163702722507 | | 2012 | 12.905126862892 | | 2011 | 12.675154530941 | | 2010 | 12.537722998038 | | 2009 | 12.16707006715 | | 2008 | 11.85828175243 | | 2007 | 11.497578950186 | | 2006 | 11.218882349562 | | 2005 | 10.928083710302 | | 2004 | 10.660278249208 | | 2003 | 10.382607559105 | | 2002 | 10.122764259117 | | 2001 | 9.9081491327695 | | 2000 | 9.7446146359397 | | 1999 | 9.647512862722 | | 1998 | 9.5520836759967 | | 1997 | 9.4940238474265 | | 1996 | 9.4678929971799 | | 1995 | 9.4185232728355 | | 1994 | 9.3715791034339 | | 1993 | 9.3639874292431 | | 1992 | 9.306674930511 | | 1991 | 9.2450105176663 |
|