| Year | Value | | 2021 | 3.9619878324416 | | 2020 | 0.42013730751569 | | 2019 | 5.8520384936233 | | 2018 | 5.9273900553951 | | 2017 | 9.0011347869582 | | 2016 | 2.6800357958836 | | 2015 | 4.6445055762247 | | 2014 | 6.317356088801 | | 2013 | 1.1453188994411 | | 2012 | 1.1085391519844 | | 2011 | 2.9057468818213 | | 2010 | -4.9728328196516 | | 2009 | -5.3575592881881 | | 2008 | 14.463136443651 | | 2007 | 13.808889554761 | | 2006 | 12.288258938966 | | 2005 | 10.758369381186 | | 2004 | 12.800255835506 | | 2003 | 3.7402622203799 | | 2002 | 3.3640213077853 | | 2001 | 5.686172997122 | | 2000 | 5.2049050257071 | | 1999 | 0.5287858643714 | | 1998 | 5.9122034637211 | | 1997 | 0.23126438737174 | | 1996 | 0.24991802214827 | | 1995 | 4.9739275004629 | | 1994 | 10.454061284444 | | 1993 | 4.6386882088529 | | 1992 | -7.303591810618 | | 1991 | -9.888849601885 |
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