| Year | Value | | 2020 | 1.3927927261936 | | 2019 | 1.4007141487214 | | 2018 | 1.3534327328102 | | 2017 | 1.3187412918694 | | 2016 | 1.2730940730995 | | 2015 | 1.2611012003457 | | 2014 | 1.5861606381122 | | 2013 | 1.5953997253052 | | 2012 | 1.5799362262527 | | 2011 | 1.5995182162133 | | 2010 | 1.6050810949178 | | 2009 | 1.6164503738994 | | 2008 | 1.6649529423755 | | 2007 | 1.6711043771794 | | 2006 | 1.7020539148787 | | 2005 | 1.154358279685 | | 2004 | 1.0937508544929 | | 2003 | 1.4265704610998 | | 2002 | 1.4517872395857 | | 2001 | 1.3884118760367 | | 2000 | 1.6666957756248 | | 1999 | 1.5688180199795 | | 1998 | 1.8631984558268 | | 1997 | 1.8154216363062 | | 1996 | 0.66619470472918 | | 1995 | 0.59243185235244 | | 1994 | 0.28388398715871 | | 1993 | 1.0089021490019 |
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