| Year | Value | | 2020 | 0.60668751649432 | | 2019 | 0.61910400173349 | | 2018 | 0.70905261011029 | | 2017 | 0.65629394093026 | | 2016 | 0.75176792164044 | | 2015 | 0.77401130926187 | | 2014 | 1.1546227874205 | | 2013 | 1.1883530348141 | | 2012 | 1.2231592401621 | | 2011 | 1.2586446446134 | | 2010 | 1.296198913746 | | 2009 | 1.331510701775 | | 2008 | 1.2697525887081 | | 2007 | 1.9534429431874 | | 2006 | 2.002002002002 | | 2005 | 2.0503707753819 | | 2004 | 2.0986358866737 | | 2003 | 3.3907451759486 | | 2002 | 2.7637213875349 | | 2001 | 2.8313634894425 | | 2000 | 2.3872045834328 | | 1999 | 2.443478146635 | | 1998 | 2.4844420211809 | | 1997 | 2.5405178261956 | | 1996 | 2.6158792307627 | | 1995 | 2.6566253927185 | | 1994 | 2.0793602699604 | | 1993 | 3.3788142205076 | | 1992 | 3.5022478063193 | | 1991 | 3.9480307551596 |
|