| Year | Value | | 2022 | 4.6368104751113 | | 2021 | 5.7169847408892 | | 2020 | 6.7183995943071 | | 2019 | 4.8187734005947 | | 2018 | 5.139013472302 | | 2017 | 5.6636304020606 | | 2016 | 6.1989974052802 | | 2015 | 6.7537200648634 | | 2014 | 7.3539501204864 | | 2013 | 7.9950691134099 | | 2012 | 8.094205335778 | | 2011 | 8.103973892215 | | 2010 | 8.3453853452786 | | 2009 | 8.0717976433557 | | 2008 | 5.9427516010212 | | 2007 | 5.6997365570228 | | 2006 | 6.2554050824951 | | 2005 | 6.7783565476241 | | 2004 | 7.0752018994512 | | 2003 | 7.2265367000694 | | 2002 | 7.2293699344802 | | 2001 | 6.6684485787143 | | 2000 | 6.641780071393 | | 1999 | 7.0368488831086 | | 1998 | 7.2228360014038 | | 1997 | 7.2945573008878 | | 1996 | 7.5878354058848 | | 1995 | 7.5935775309875 | | 1994 | 8.0090808417433 | | 1993 | 7.9689730882168 | | 1992 | 7.4605605479471 | | 1991 | 6.7747373961029 |
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