Year | Value | 2021 | 31.661361282935 | 2020 | 31.509048373046 | 2019 | 31.356735463157 | 2018 | 31.204422553268 | 2017 | 31.05210964338 | 2016 | 30.899796733491 | 2015 | 30.747483823602 | 2014 | 30.595170913713 | 2013 | 30.442858003824 | 2012 | 30.290545093935 | 2011 | 30.138232184047 | 2010 | 29.985919274158 | 2009 | 29.779365435927 | 2008 | 29.572811597697 | 2007 | 29.366257759466 | 2006 | 29.159703921236 | 2005 | 28.953150083005 | 2004 | 28.746071257033 | 2003 | 28.52389357271 | 2002 | 28.332971124995 | 2001 | 28.126421058975 | 2000 | 27.919870992956 | 1999 | 27.764324300632 | 1998 | 27.608726619257 | 1997 | 27.453128937882 | 1996 | 27.297531256506 | 1995 | 27.141933575131 | 1994 | 26.986335893755 | 1993 | 26.83073821238 | 1992 | 26.675140531005 | 1991 | 26.519542849629 | 1990 | 26.363945168254 |
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