| Year | Value | | 2022 | 19.200551495398 | | 2021 | 19.369002709544 | | 2020 | 20.413364368378 | | 2019 | 21.387956720924 | | 2018 | 20.024133741192 | | 2017 | 20.694523926283 | | 2016 | 20.569644479384 | | 2015 | 20.753614890775 | | 2014 | 19.616330295024 | | 2013 | 19.61645588634 | | 2012 | 17.445361834224 | | 2011 | 17.469295334227 | | 2010 | 17.525868116408 | | 2009 | 18.183481820315 | | 2008 | 15.717329062717 | | 2007 | 18.0473595021 | | 2006 | 17.008090074918 | | 2005 | 17.691074629735 | | 2004 | 20.0302441455 | | 2003 | 21.33572259414 | | 2002 | 20.853637142055 | | 2001 | 21.788859991337 | | 2000 | 19.774605314603 |
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