| Year | Value | | 2019 | 21.199395222959 | | 2018 | 21.796415970729 | | 2017 | 20.673766025812 | | 2016 | 19.526194721247 | | 2015 | 21.465487310151 | | 2014 | 23.422298313654 | | 2013 | 25.972191627023 | | 2012 | 24.51342329878 | | 2011 | 24.619132583036 | | 2010 | 24.894922750589 | | 2009 | 23.945648962338 | | 2008 | 23.484959922762 | | 2007 | 21.026805231976 | | 2006 | 21.325395288831 | | 2005 | 21.871421347966 | | 2004 | 20.800942248396 |
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