| Year | Value | | 2021 | 13.336675438252 | | 2020 | 11.89744760342 | | 2019 | 13.096518405414 | | 2018 | 13.836908087278 | | 2017 | 13.544708994309 | | 2016 | 13.632149681212 | | 2015 | 14.540723185769 | | 2014 | 34.438528502215 | | 2013 | 33.487977633635 | | 2012 | 34.071221351163 | | 2011 | 30.490738972694 | | 2010 | 37.07563520203 | | 2009 | 30.82052630321 | | 2008 | 30.538698477046 | | 2007 | 32.679471461654 | | 2006 | 29.94854654998 | | 2005 | 27.749360613811 | | 2004 | 29.700338327694 | | 2003 | 29.308461473826 | | 2002 | 29.849307450805 | | 2001 | 30.278511200068 | | 1995 | 33.939804509823 | | 1990 | 31.425953910087 |
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