| Year | Value | | 2022 | 32.567269399468 | | 2021 | 32.652751566644 | | 2020 | 33.007325855281 | | 2019 | 31.333031481977 | | 2018 | 30.931697782422 | | 2017 | 28.856870717815 | | 2016 | 28.46944740499 | | 2015 | 28.072939959333 | | 2014 | 32.991551838695 | | 2013 | 33.201341868005 | | 2012 | 34.865017516768 | | 2011 | 35.765899697637 | | 2010 | 33.436208245426 | | 2009 | 27.502746171332 | | 2008 | 27.900472557419 | | 2007 | 31.840216892624 | | 2006 | 33.330763377655 | | 2005 | 33.07503365253 | | 2004 | 33.466382686036 | | 2003 | 31.493220573482 | | 2002 | 32.527674508457 | | 2001 | 31.301895580413 | | 2000 | 31.247793312653 | | 1999 | 26.8713762086 | | 1998 | 23.344799829371 | | 1997 | 21.795506172379 | | 1996 | 21.196503227514 |
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