| Year | Value | | 2021 | 4.629 | | 2020 | 3.67 | | 2019 | 3.567 | | 2018 | 3.521 | | 2017 | 3.421 | | 2016 | 3.473 | | 2015 | 3.451 | | 2014 | 3.427 | | 2013 | 3.39 | | 2012 | 3.363 | | 2011 | 3.304 | | 2010 | 3.356 | | 2009 | 3.303 | | 2008 | 3.367 | | 2007 | 3.387 | | 2006 | 3.169 | | 2005 | 3.035 | | 2004 | 3.151 | | 2003 | 3.149 | | 2002 | 3.203 | | 2001 | 3.225 | | 2000 | 3.24 | | 1999 | 3.3192 |
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