| Year | Value | | 2022 | 2.236 | | 2021 | 2.118 | | 2020 | 1.989 | | 2019 | 1.884 | | 2018 | 1.814 | | 2017 | 1.805 | | 2016 | 1.774 | | 2015 | 1.765 | | 2014 | 1.738 | | 2013 | 1.751 | | 2012 | 1.726 | | 2011 | 1.698 | | 2010 | 1.683 | | 2009 | 1.637 | | 2008 | 1.581 | | 2007 | 1.532 | | 2006 | 1.492 | | 2005 | 1.455 | | 2004 | 1.416 | | 2003 | 1.393 | | 2002 | 1.371 | | 2001 | 1.356 | | 2000 | 1.303 | | 1999 | 1.233 | | 1998 | 1.178 | | 1997 | 1.138 | | 1996 | 1.116 | | 1995 | 1.112 | | 1994 | 1.097 | | 1993 | 1.035 | | 1992 | 0.983 | | 1991 | 0.956 | | 1990 | 0.904 |
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