| Year | Value | | 2021 | 6.3363649163329 | | 2020 | -1.0961787310764 | | 2019 | 3.6578161350715 | | 2018 | 3.8491013290217 | | 2017 | 6.0587352791553 | | 2016 | 4.5137155010456 | | 2015 | 3.5862762877531 | | 2014 | 5.5988622375135 | | 2013 | 4.7285318873274 | | 2012 | 7.1315181928144 | | 2011 | 5.2949320691811 | | 2010 | 8.0013627447216 | | 2009 | 3.8853474336903 | | 2008 | 5.5540155114806 | | 2007 | 12.467669332007 | | 2006 | 11.493232336551 | | 2005 | 9.1829094535261 | | 2004 | 9.6444537632016 | | 2003 | 7.3624448890139 | | 2002 | 7.084409040425 | | 2001 | 6.0427830925524 | | 2000 | 7.8562174510056 | | 1999 | 5.3153928477533 | | 1998 | 3.5023907367291 | | 1997 | 5.9267176381718 | | 1996 | 8.2587554772834 |
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