| Year | Value | | 2022 | 11.094305376995 | | 2021 | 10.848207357906 | | 2020 | 10.666636178682 | | 2019 | 11.110927271503 | | 2018 | 9.9033488999281 | | 2017 | 8.8789490177227 | | 2016 | 8.0817354172421 | | 2015 | 7.5097900534894 | | 2014 | 7.0281257150866 | | 2013 | 6.6428286269129 | | 2012 | 6.4930489405735 | | 2011 | 6.5878960336669 | | 2010 | 6.5044165290081 | | 2009 | 6.3995055572381 | | 2008 | 6.34404082858 | | 2007 | 6.2263352541498 | | 2006 | 6.1132614988895 | | 2005 | 6.0123695795832 | | 2004 | 5.9265968597561 | | 2003 | 5.8473111729824 | | 2002 | 5.7699581932118 | | 2001 | 5.7036087395325 | | 2000 | 5.6427392129322 | | 1999 | 5.5922662436004 | | 1998 | 5.5485291473971 | | 1997 | 5.4999745416688 | | 1996 | 5.4532183699907 | | 1995 | 5.4616209879818 | | 1994 | 5.4688201353127 | | 1993 | 5.4737683398691 | | 1992 | 5.462542751711 | | 1991 | 5.4542137244643 |
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