| Year | Value | | 2020 | 1.1835595876507 | | 2019 | 1.303912572386 | | 2018 | 1.3213733661142 | | 2017 | 1.3709369619362 | | 2016 | 1.4449109459616 | | 2015 | 1.4848074023986 | | 2014 | 1.5201380310509 | | 2013 | 1.5711167995111 | | 2012 | 1.6286575556672 | | 2011 | 1.6580767904963 | | 2010 | 1.7080737457657 | | 2009 | 1.6859964898733 | | 2008 | 1.6053927716382 | | 2007 | 1.6192513328375 | | 2005 | 1.7191993145634 | | 2004 | 1.7705044466519 | | 2003 | 1.8843084012178 | | 2002 | 1.9781273509369 | | 2001 | 2.0048572972392 | | 2000 | 2.3533342082098 | | 1999 | 2.3602849481638 | | 1998 | 2.2960864817533 | | 1997 | 2.3753683007635 | | 1996 | 2.4309082004185 | | 1995 | 2.5057254099434 | | 1994 | 1.7507903833709 | | 1993 | 1.9048681568046 | | 1992 | 2.0133565143016 | | 1991 | 2.1474313424125 |
|