| Year | Value | | 2022 | 13.414319143278 | | 2021 | 13.200639692158 | | 2020 | 13.063132087037 | | 2019 | 13.323408082876 | | 2018 | 13.999944487028 | | 2017 | 14.610545938043 | | 2016 | 15.144840871328 | | 2015 | 16.003829515637 | | 2014 | 16.939932220668 | | 2013 | 17.438081619857 | | 2012 | 18.073541018371 | | 2011 | 18.316386314287 | | 2010 | 18.545136457029 | | 2009 | 18.805333949506 | | 2008 | 18.908840571396 | | 2007 | 18.314389302352 | | 2006 | 17.797308237557 | | 2005 | 17.06536633449 | | 2004 | 15.973924957259 | | 2003 | 14.56764954087 | | 2002 | 13.467406257716 | | 2001 | 12.167889955107 | | 2000 | 10.616561875518 | | 1999 | 9.4739951514658 | | 1998 | 8.3652462762356 | | 1997 | 7.4203222746736 | | 1996 | 6.5008094061515 | | 1995 | 5.9687716781696 | | 1994 | 5.7136255009152 | | 1993 | 5.4928083073311 | | 1992 | 5.3414153973682 | | 1991 | 5.2275153456098 |
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