| Year | Value | | 2022 | 2.4255377762386 | | 2021 | 2.4570386527757 | | 2020 | 2.4865499384832 | | 2019 | 2.5117824626467 | | 2018 | 2.5330114844554 | | 2017 | 1.9886863487128 | | 2016 | 2.2461052758018 | | 2015 | 2.2904800584415 | | 2014 | 2.3440772109436 | | 2013 | 2.4008483198368 | | 2012 | 2.4676871500323 | | 2011 | 2.5251868307924 | | 2010 | 2.5970322179898 | | 2009 | 2.66795074941 | | 2008 | 2.7513588022909 | | 2007 | 2.5552519602694 | | 2006 | 2.5552586751927 | | 2005 | 2.5552623734323 | | 2004 | 2.5552758918189 | | 2003 | 2.555247555623 | | 2002 | 2.555284566234 | | 2001 | 2.5552675698799 | | 2000 | 2.5552356984485 | | 1999 | 2.5552683703916 | | 1998 | 2.5552694776993 | | 1997 | 4.4778720446917 | | 1996 | 4.477878002249 | | 1995 | 4.477872882206 | | 1994 | 4.4778524975439 | | 1993 | 4.4778842348997 | | 1992 | 4.4778860733677 | | 1991 | 4.4778876026941 |
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