| Year | Value | | 2020 | 2.9223178486914 | | 2019 | 3.0117349235852 | | 2018 | 1.1436448698193 | | 2017 | 0.98335613091989 | | 2016 | 0.84949558916547 | | 2015 | 1.0344927764087 | | 2014 | 0.82524944678017 | | 2013 | 1.069895478813 | | 2012 | 1.1819776293188 | | 2011 | 1.1141542707948 | | 2010 | 1.1762284357258 | | 2009 | 1.3631667858969 | | 2008 | 1.2358155844962 | | 2007 | 1.1450979624208 | | 2006 | 1.1661748917401 | | 2005 | 1.1618456290888 | | 2004 | 4.2168406661192 | | 2003 | 3.3068131878688 | | 2002 | 3.578992891915 | | 2001 | 4.1036429089939 | | 2000 | 3.7327777207166 | | 1999 | 4.4087966232009 | | 1998 | 4.9815184530649 | | 1997 | 4.4833347227864 | | 1996 | 4.4350730792329 | | 1995 | 4.2185758088069 | | 1994 | 4.5498158836971 | | 1993 | 4.7047427585193 | | 1992 | 4.7409478173769 | | 1991 | 4.4335436133512 | | 1990 | 4.5621039933317 |
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