| Year | Value | | 2021 | 15.059305980115 | | 2020 | 15.123989533793 | | 2019 | 15.18867856501 | | 2018 | 15.25348958209 | | 2017 | 15.318290551966 | | 2016 | 15.382897618115 | | 2015 | 15.447844112531 | | 2014 | 15.512544216909 | | 2013 | 15.576763602424 | | 2012 | 15.64130887777 | | 2011 | 15.70608868877 | | 2010 | 15.770829444492 | | 2009 | 15.835264101689 | | 2008 | 15.900232598752 | | 2007 | 15.964029924858 | | 2006 | 16.028963389221 | | 2005 | 16.093836404357 | | 2004 | 16.158553674083 | | 2003 | 18.3095 | | 2002 | 18.3825 | | 2001 | 18.4555 | | 2000 | 18.5285 | | 1999 | 18.6015 | | 1998 | 18.6745 | | 1997 | 18.7475 | | 1996 | 18.8205 | | 1995 | 18.8935 | | 1994 | 18.9665 | | 1993 | 19.0395 | | 1992 | 18.398038147139 | | 1991 | 18.467211625795 | | 1990 | 18.53638510445 |
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