| Year | Value | | 2020 | 1.7017132793633 | | 2019 | 1.9239990764804 | | 2018 | 1.9460278950077 | | 2017 | 1.9739045711937 | | 2016 | 2.0069358802967 | | 2015 | 2.0239673748744 | | 2014 | 1.9496309475882 | | 2013 | 1.9745535396889 | | 2012 | 1.9184780195239 | | 2011 | 1.9697899379648 | | 2010 | 2.0278126854915 | | 2009 | 2.0722002036893 | | 2008 | 2.0526821113599 | | 2007 | 2.1040254768305 | | 2006 | 2.0568523285972 | | 2005 | 1.7533620717726 | | 2004 | 1.7542240252675 | | 2003 | 1.606012031698 | | 2002 | 1.4318177493384 | | 2001 | 1.439996613321 | | 2000 | 1.3838968529569 | | 1999 | 1.3258767402993 | | 1998 | 1.3568320594349 | | 1997 | 1.3870146652574 | | 1996 | 1.4242568834402 | | 1995 | 1.4595585954619 | | 1994 | 0.94009508095893 | | 1993 | 0.92252085793112 | | 1992 | 0.95049669606665 | | 1991 | 0.77333534119309 | | 1990 | 0.79263832115168 |
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