| Year | Value | | 2021 | 12.808979703101 | | 2020 | 13.943418907646 | | 2019 | 12.392711748947 | | 2018 | 12.572796347236 | | 2017 | 13.502165595807 | | 2016 | 12.087573410896 | | 2015 | 11.769720304912 | | 2014 | 12.384249823799 | | 2013 | 12.639092410007 | | 2012 | 12.803489882729 | | 2011 | 13.862109592122 | | 2010 | 10.103053954238 | | 2009 | 10.20378859028 | | 2008 | 10.0081952087 | | 2007 | 8.2715294160384 | | 2006 | 5.6415269434507 | | 2003 | 9.4133460922086 | | 2002 | 11.464890095225 | | 2001 | 12.735816697537 | | 2000 | 10.074059282664 | | 1999 | 5.5230994290029 | | 1998 | 0.94776534899023 | | 1997 | 7.3322316060548 | | 1996 | 18.168348267833 | | 1995 | 15.03305953858 | | 1994 | 17.427779061706 | | 1993 | 16.495750068952 | | 1992 | 23.295819935691 |
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