| Year | Value | | 2020 | 1.1457633807658 | | 2019 | 1.0071208315959 | | 2018 | 1.0396563229087 | | 2017 | 1.0727118709756 | | 2016 | 1.1133413766202 | | 2015 | 2.4463145942057 | | 2014 | 2.528376070829 | | 2013 | 2.6006909198397 | | 2012 | 2.6579381439567 | | 2011 | 2.7082640171107 | | 2010 | 1.3199607842566 | | 2009 | 1.3494646148135 | | 2008 | 1.3912257038041 | | 2007 | 1.4347064528464 | | 2005 | 1.4824910574452 | | 2004 | 1.5019230821746 | | 2003 | 1.4584320747043 | | 2002 | 1.6180775802955 | | 2001 | 1.6587188617336 | | 2000 | 1.6429402719032 | | 1999 | 1.5535011199511 | | 1998 | 1.5963143618817 | | 1997 | 1.4144818746918 | | 1996 | 1.5962502852914 | | 1995 | 2.122348713499 | | 1994 | 1.3503632806582 | | 1993 | 1.3930792164303 | | 1992 | 1.423409955607 | | 1991 | 1.1498087602691 |
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