| Year | Value | | 2021 | 29.350626719209 | | 2020 | 23.794985059567 | | 2019 | 29.823392522298 | | 2018 | 31.546794416282 | | 2017 | 28.21912391123 | | 2016 | 24.690682645503 | | 2015 | 24.919807421957 | | 2014 | 33.134918576413 | | 2013 | 36.419726723912 | | 2012 | 38.277936990253 | | 2011 | 39.219250058509 | | 2010 | 35.34620465205 | | 2009 | 30.81964617539 | | 2008 | 42.458193339566 | | 2007 | 39.961522413815 | | 2006 | 40.529734655723 | | 2005 | 39.013342857973 | | 2000 | 30.085819647277 | | 1999 | 26.782027556686 | | 1998 | 22.064207324479 | | 1997 | 26.023355066311 | | 1996 | 26.496082695265 | | 1995 | 24.766456610486 |
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