| Year | Value | | 2020 | 1.3060107959601 | | 2019 | 1.2618940685816 | | 2018 | 1.2736562926113 | | 2017 | 1.2655781160834 | | 2016 | 1.4602418321129 | | 2015 | 1.4606818313564 | | 2014 | 1.4477658043974 | | 2013 | 1.4792202968786 | | 2012 | 1.4794653694652 | | 2011 | 1.4707208092258 | | 2010 | 1.5194919536632 | | 2009 | 1.5181888440961 | | 2008 | 1.5725609367363 | | 2007 | 1.5858748150833 | | 2005 | 1.6510855954045 | | 2004 | 1.6581662358229 | | 2003 | 1.6735906719836 | | 2002 | 1.6480135456081 | | 2001 | 1.6108979846887 | | 2000 | 1.6420394129509 | | 1999 | 1.7910859032354 | | 1998 | 1.7661549567885 | | 1997 | 1.7559031712083 | | 1996 | 1.8095793069284 | | 1995 | 1.8541024290141 | | 1994 | 1.7936396104502 | | 1993 | 1.8559417976652 | | 1992 | 1.8386516946485 | | 1991 | 1.8579362490051 |
|