| Year | Value | | 2021 | 1.5227102023261 | | 2020 | 1.519450054025 | | 2019 | 1.5133820243223 | | 2018 | 1.6641454630766 | | 2017 | 1.5668728010359 | | 2016 | 1.7155703421043 | | 2015 | 1.6513439836558 | | 2014 | 1.6258285608912 | | 2013 | 1.6183163815579 | | 2012 | 1.504850207395 | | 2011 | 1.5020202394633 | | 2010 | 1.7954462094322 | | 2009 | 1.9851507615 | | 2008 | 2.3341543675301 | | 2007 | 2.5472540722704 | | 2006 | 3.092044852969 | | 2005 | 4.2001166354398 | | 2004 | 5.3767470264119 | | 2003 | 6.0393583085482 | | 2002 | 5.4861723926472 | | 2001 | 5.0891728111429 | | 2000 | 7.3889835554004 | | 1999 | 11.135252708263 | | 1998 | 8.1625762339882 | | 1997 | 11.72032193159 | | 1996 | 12.4715261959 |
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