| Year | Value | | 2021 | 31.480368573763 | | 2020 | 31.54148207007 | | 2019 | 31.595556337019 | | 2018 | 31.651776456961 | | 2017 | 31.705196578455 | | 2016 | 31.774579227824 | | 2015 | 31.820733319524 | | 2014 | 31.883914253359 | | 2013 | 31.945336441773 | | 2012 | 32.006025692209 | | 2011 | 32.110231017514 | | 2010 | 32.172279071142 | | 2009 | 32.234890695742 | | 2008 | 32.296277202335 | | 2007 | 32.358249474564 | | 2006 | 32.420448553365 | | 2005 | 32.482180954423 | | 2004 | 32.54602021871 | | 2003 | 32.660179124594 | | 2002 | 32.725428321699 | | 2001 | 32.787354779069 | | 2000 | 32.849966774736 | | 1999 | 32.957799237378 | | 1998 | 33.048611350293 | | 1997 | 33.127772219901 | | 1996 | 33.216390694838 | | 1995 | 33.304608505767 | | 1994 | 33.391917016455 | | 1993 | 33.47605370215 | | 1992 | 33.5630743408 |
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