| Year | Value | | 2021 | 56.011273957159 | | 2020 | 55.95603156708 | | 2019 | 55.900789177001 | | 2018 | 55.845546786922 | | 2017 | 55.790304396843 | | 2016 | 55.735062006764 | | 2015 | 55.679819616685 | | 2014 | 55.625028184893 | | 2013 | 55.5702367531 | | 2012 | 55.515445321308 | | 2011 | 55.460653889515 | | 2010 | 55.405862457723 | | 2009 | 54.703494926719 | | 2008 | 54.001127395716 | | 2007 | 53.298759864713 | | 2006 | 52.596392333709 | | 2005 | 51.894024802706 | | 2004 | 51.191657271702 | | 2003 | 50.489289740699 | | 2002 | 49.786922209696 | | 2001 | 49.084554678692 | | 2000 | 48.382187147689 | | 1999 | 47.155355129651 | | 1998 | 45.928523111612 | | 1997 | 44.701691093574 | | 1996 | 43.474859075535 | | 1995 | 42.248027057497 | | 1994 | 41.021195039459 | | 1993 | 39.794363021421 | | 1992 | 38.567531003382 | | 1991 | 37.340698985344 | | 1990 | 36.113866967305 |
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