| Year | Value | | 2022 | 3.640641637095 | | 2021 | 3.4575872147227 | | 2020 | 3.3305285403988 | | 2019 | 3.287457574992 | | 2018 | 3.2591557318566 | | 2017 | 3.4232328573947 | | 2016 | 3.7629757785467 | | 2015 | 5.3573669547466 | | 2014 | 6.394992795389 | | 2013 | 7.4305213803248 | | 2012 | 7.5841945288754 | | 2011 | 7.5777404290089 | | 2010 | 7.8960848324528 | | 2009 | 8.0488809042593 | | 2008 | 8.589195491644 | | 2007 | 7.6305659450162 | | 2006 | 7.2771695075866 | | 2005 | 9.8418126176348 | | 2004 | 7.9528971677227 | | 2003 | 9.8186304750154 | | 2002 | 9.3064876957494 | | 2001 | 7.9567017422805 | | 2000 | 5.8414582450191 | | 1999 | 5.4276936344527 | | 1998 | 5.5902504092645 | | 1997 | 6.2197141630375 | | 1996 | 3.5536225734592 |
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