| Year | Value | | 2020 | 1.1635071829718 | | 2019 | 1.1759206723914 | | 2018 | 1.2274292599701 | | 2017 | 1.1891714051844 | | 2016 | 1.2557900765284 | | 2015 | 1.1500598714579 | | 2014 | 1.2153898159245 | | 2013 | 1.2551190178953 | | 2012 | 1.2973307407947 | | 2011 | 1.3289316344544 | | 2010 | 1.3601331691756 | | 2009 | 1.369462497739 | | 2008 | 1.4440685217366 | | 2007 | 1.5311328481465 | | 2005 | 1.7150877988071 | | 2004 | 1.6998682315947 | | 2003 | 1.8243740551727 | | 2002 | 1.8458629775435 | | 2001 | 1.85493525777 | | 2000 | 1.841196383719 | | 1999 | 1.894882326344 | | 1998 | 1.9250985545335 | | 1997 | 1.82976756227 | | 1996 | 1.9221816285659 | | 1995 | 1.9232709624596 | | 1994 | 1.3661664106812 | | 1993 | 1.4263417135548 | | 1992 | 1.4928363758445 | | 1991 | 1.7557072223466 |
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