| Year | Value | | 2021 | 9.5762285056479 | | 2020 | 9.1385849347633 | | 2019 | 9.4721203637706 | | 2018 | 8.4358853940114 | | 2017 | 7.5718466838746 | | 2016 | 6.8037111151537 | | 2015 | 4.5503830288745 | | 2014 | 4.3541502730286 | | 2013 | 3.8191948238677 | | 2012 | 3.2806804374241 | | 2011 | 3.6297099059197 | | 2010 | 4.2167041140466 | | 2009 | 4.0878499462387 | | 2008 | 3.6033985738128 | | 1999 | 11.774475931806 | | 1998 | 12.836817459539 | | 1997 | 8.932601336047 | | 1996 | 19.645314399332 | | 1995 | 8.5557446541931 | | 1994 | 8.3533291149021 |
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