| Year | Value | | 2020 | 1.9900110206099 | | 2019 | 1.9755831241342 | | 2018 | 1.9516432467016 | | 2017 | 1.9487847571257 | | 2016 | 1.933982329387 | | 2015 | 1.9834494851558 | | 2014 | 1.7062864524833 | | 2013 | 1.6663505670174 | | 2012 | 1.7968254862359 | | 2011 | 1.7929981057843 | | 2010 | 1.8847971641263 | | 2009 | 1.9682956676588 | | 2008 | 1.9441997546699 | | 2007 | 1.9583704834401 | | 2006 | 1.9437789495864 | | 2005 | 1.9616924428595 | | 2004 | 1.9727029270387 | | 2003 | 1.8805078856806 | | 2002 | 1.9145843780165 | | 2001 | 1.9219225547844 | | 2000 | 1.9471570953819 | | 1999 | 2.0327348348086 | | 1998 | 2.4757171710448 | | 1997 | 2.6281714752858 | | 1996 | 2.2973189310793 | | 1995 | 2.5165438642194 | | 1994 | 1.9505475723436 | | 1993 | 2.0322357846563 | | 1992 | 2.5039615967146 |
|