| Year | Value | | 2020 | 1.5874828909999 | | 2019 | 1.5794511099207 | | 2018 | 1.6637776421581 | | 2017 | 1.693683675244 | | 2016 | 1.722797924738 | | 2015 | 1.7712412240347 | | 2014 | 1.8085030317529 | | 2013 | 1.8506056527591 | | 2012 | 1.8798919916601 | | 2011 | 1.9174192449463 | | 2010 | 1.9539805856266 | | 2009 | 1.9785914186988 | | 2008 | 2.0359736684049 | | 2007 | 2.0586158218685 | | 2006 | 2.0030113565859 | | 2005 | 1.9923726144983 | | 2004 | 1.968839349758 | | 2003 | 1.9495695398298 | | 2002 | 2.0713997953809 | | 2001 | 2.0561273184252 | | 2000 | 2.0405294599977 | | 1999 | 2.0096510592447 | | 1998 | 2.0917449160878 | | 1997 | 2.5893376076413 | | 1996 | 2.7235259500111 | | 1995 | 3.1718891015443 | | 1994 | 1.2931434688367 | | 1993 | 1.2127944968237 | | 1992 | 1.2091517603562 |
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