| Year | Value | | 2020 | 1.1519426617675 | | 2019 | 1.1332183946207 | | 2018 | 1.1361269499538 | | 2017 | 1.1401779433902 | | 2016 | 1.1550601889056 | | 2015 | 1.1653411483551 | | 2014 | 1.1384575719849 | | 2013 | 1.118371079009 | | 2012 | 1.1784078668656 | | 2011 | 1.180616104607 | | 2010 | 1.2401220891479 | | 2009 | 1.255514653823 | | 2008 | 1.2939261721987 | | 2007 | 1.3073450744649 | | 2006 | 1.3259426070821 | | 2005 | 1.4452619974084 | | 2004 | 1.4146728315333 | | 2003 | 1.489267406707 | | 2002 | 1.5385292997833 | | 2001 | 1.5830392541816 | | 2000 | 1.6576450887519 | | 1999 | 1.757501043802 | | 1998 | 1.8793919900075 | | 1997 | 1.9360983054503 | | 1996 | 1.9255060071126 | | 1995 | 1.9836616240693 | | 1994 | 1.6579850118826 | | 1993 | 1.6603455943542 | | 1992 | 1.8703275268062 |
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