| Year | Value | | 2021 | 39.826143216713 | | 2020 | 40.529222250189 | | 2019 | 41.232318147496 | | 2018 | 41.935388874906 | | 2017 | 42.638484772212 | | 2016 | 43.627309338032 | | 2015 | 44.044651396929 | | 2014 | 45.08732443997 | | 2013 | 46.12999748301 | | 2012 | 47.172670526051 | | 2011 | 48.215343569091 | | 2010 | 49.258016612132 | | 2009 | 50.119189529323 | | 2008 | 50.980362446514 | | 2007 | 51.841535363705 | | 2006 | 52.702708280896 | | 2005 | 53.563881198087 | | 2004 | 54.425054115278 | | 2003 | 55.286227032469 | | 2002 | 56.14739994966 | | 2001 | 57.008572866851 | | 2000 | 57.869745784042 | | 1999 | 58.512637805185 | | 1998 | 59.155529826328 | | 1997 | 59.79842184747 | | 1996 | 60.441313868613 | | 1995 | 61.084205889756 | | 1994 | 61.727097910899 | | 1993 | 62.369989932041 | | 1992 | 63.012881953184 | | 1991 | 63.655773974327 | | 1990 | 64.298665995469 |
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