| Year | Value | | 2021 | 2.362 | | 2020 | 2.325 | | 2019 | 2.259 | | 2018 | 2.202 | | 2017 | 2.131 | | 2016 | 2.057 | | 2015 | 1.991 | | 2014 | 1.93 | | 2013 | 1.853 | | 2012 | 1.785 | | 2011 | 1.726 | | 2010 | 1.664 | | 2009 | 1.616 | | 2008 | 1.561 | | 2007 | 1.509 | | 2006 | 1.467 | | 2005 | 1.429 | | 2004 | 1.387 | | 2003 | 1.348 | | 2002 | 1.317 | | 2001 | 1.285 | | 2000 | 1.26 | | 1999 | 1.218 | | 1998 | 1.18 | | 1997 | 1.133 | | 1996 | 1.09 | | 1995 | 1.049 | | 1994 | 1.003 | | 1993 | 0.958 | | 1992 | 0.917 | | 1991 | 0.859 | | 1990 | 0.803 | | 1977 | 0.478 | | 1970 | 0.42 | | 1965 | 0.377 | | 1960 | 0.354 |
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