| Year | Value | | 2022 | 16.975712792262 | | 2021 | 9.3225805248891 | | 2020 | 17.352023126148 | | 2019 | 21.200162409736 | | 2018 | 23.868660807006 | | 2017 | 22.227172700223 | | 2016 | 20.515526485676 | | 2015 | 18.29515366949 | | 2014 | 18.158578049163 | | 2013 | 20.563965284247 | | 2012 | 19.245346136447 | | 2011 | 18.291796674434 | | 2010 | 10.591566085531 | | 2009 | 10.351034320844 | | 2008 | 10.978807853143 | | 2007 | 13.496063861675 | | 2006 | 14.550007646429 | | 2005 | 14.298947502915 | | 2004 | 12.468401231277 | | 2003 | 15.746639661204 | | 2002 | 18.500644601887 | | 2001 | 19.596757814664 | | 2000 | 20.977560686583 | | 1999 | 16.865692515215 | | 1998 | 18.538386596264 | | 1997 | 18.562124001851 | | 1996 | 17.358542065732 | | 1995 | 16.693401801163 | | 1994 | 14.139799425306 | | 1993 | 12.846735024285 | | 1992 | 12.114918413277 | | 1991 | 10.408644467439 | | 1990 | 8.8892142658981 |
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