| Year | Value | | 2020 | 1.6325827289775 | | 2019 | 1.5398863497707 | | 2018 | 1.5580648992131 | | 2017 | 1.5916773677437 | | 2016 | 1.6423798147671 | | 2015 | 1.6944611242961 | | 2014 | 2.0953508411613 | | 2013 | 2.1443903249504 | | 2012 | 2.2255070564335 | | 2011 | 2.2712260491838 | | 2010 | 2.3756580646497 | | 2009 | 2.481560804557 | | 2008 | 2.5788439467486 | | 2007 | 2.6587463828342 | | 2006 | 2.6958187454814 | | 2005 | 2.7153145412443 | | 2004 | 2.7731021694573 | | 2003 | 2.928417503532 | | 2002 | 2.9134828386526 | | 2001 | 2.9609864327521 | | 2000 | 3.7532521269903 | | 1999 | 3.6908328172076 | | 1998 | 3.6726421789269 | | 1997 | 3.7704291650134 | | 1996 | 3.2473315470867 | | 1995 | 3.2185631046875 | | 1994 | 3.8387187180516 | | 1993 | 3.4897490402427 | | 1992 | 3.4209298709377 | | 1991 | 3.9365469755642 |
|