Year | Value | 2021 | 2.789 | 2020 | 2.648 | 2019 | 2.633 | 2018 | 2.514 | 2017 | 2.409 | 2016 | 2.267 | 2015 | 2.237 | 2014 | 2.14 | 2013 | 2.159 | 2012 | 1.996 | 2011 | 1.966 | 2010 | 1.92 | 2009 | 1.647 | 2008 | 1.673 | 2001 | 0.655 | 2000 | 0.694 | 1997 | 1.66 | 1993 | 1.335 | 1990 | 1.433 | 1986 | 1.346 | 1981 | 0.55 | 1970 | 0.134 | 1965 | 0.106 | 1960 | 0.061 |
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