| Year | Value | | 2021 | 56.65170261526 | | 2020 | 56.805607980588 | | 2019 | 56.959423025074 | | 2018 | 57.113372876786 | | 2017 | 57.313545601727 | | 2016 | 57.467620075553 | | 2015 | 57.621559633028 | | 2014 | 57.775580140313 | | 2013 | 57.758165186979 | | 2012 | 57.911729889696 | | 2011 | 58.065294592413 | | 2010 | 58.21885929513 | | 2009 | 58.372410546139 | | 2008 | 58.525961797148 | | 2007 | 58.679513048157 | | 2006 | 58.833064299166 | | 2005 | 58.986615550175 | | 2004 | 59.140166801184 | | 2003 | 59.293718052193 | | 2002 | 59.447269303202 | | 2001 | 59.60082055421 | | 2000 | 59.754371805219 | | 1999 | 59.976674737692 | | 1998 | 60.198977670164 | | 1997 | 60.421280602637 | | 1996 | 60.643583535109 | | 1995 | 60.865886467581 | | 1994 | 61.088189400054 | | 1993 | 61.310492332526 | | 1992 | 61.532795264999 | | 1991 | 61.755098197471 | | 1990 | 61.977401129944 |
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