| Year | Value | | 2022 | 1.9735755573905 | | 2021 | 0.98101513554488 | | 2020 | 2.4194218945778 | | 2019 | 2.8992341635823 | | 2018 | 2.0747903996558 | | 2017 | 1.5931360007144 | | 2016 | 2.0000018219194 | | 2015 | 1.4370238093565 | | 2014 | 1.9216416278852 | | 2013 | 2.6210500174812 | | 2012 | 2.6195243264554 | | 2011 | 5.5538989225749 | | 2010 | 3.175324752692 | | 2009 | 0.7281652509329 | | 2008 | 5.9252513704109 | | 2007 | 4.8167676737883 | | 2006 | 1.6494309945586 | | 2005 | 1.7764140766757 | | 2004 | 3.8246374310816 | | 2003 | 1.1276034872964 | | 2002 | 0.73197090235024 | | 2001 | 0.71912560912011 | | 2000 | 0.34781122686459 | | 1999 | -1.4014726827646 | | 1998 | 0.77318601154932 | | 1997 | 2.7864650553188 | | 1996 | 8.3131602889391 | | 1995 | 16.791225165092 | | 1994 | 24.256989724336 | | 1993 | 14.61007863566 | | 1992 | 6.3539813402487 | | 1991 | 3.5566856522045 | | 1990 | 3.0522901207523 | | 1989 | 18.245638362165 | | 1988 | 18.811817944875 | | 1987 | 7.2338355306561 |
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