| Year | Value | | 2022 | 5.0509556366251 | | 2021 | 6.2667024353611 | | 2020 | 7.2873665789239 | | 2019 | 5.3890393135242 | | 2018 | 5.4695128200529 | | 2017 | 5.9073503926987 | | 2016 | 6.4354300690023 | | 2015 | 6.8522234741191 | | 2014 | 7.4018904177816 | | 2013 | 7.9747922858752 | | 2012 | 8.0853995679007 | | 2011 | 8.1020052926771 | | 2010 | 8.5010744261865 | | 2009 | 8.3557331141281 | | 2008 | 6.1966363214547 | | 2007 | 5.8768700865427 | | 2006 | 6.1740055036279 | | 2005 | 6.8216390800777 | | 2004 | 7.1803185577374 | | 2003 | 7.2538604001353 | | 2002 | 7.1739744749342 | | 2001 | 6.6858034445283 | | 2000 | 6.7809779591309 | | 1999 | 7.1803729815877 | | 1998 | 7.2349712178776 | | 1997 | 7.2628330965788 | | 1996 | 7.5574020994851 | | 1995 | 7.5999519017691 | | 1994 | 7.8351443613896 | | 1993 | 7.6366753006556 | | 1992 | 7.2805902312623 | | 1991 | 6.6817827271081 |
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