| Year | Value | | 2021 | 24.252455409789 | | 2020 | 24.342651373337 | | 2019 | 24.432810243319 | | 2018 | 24.523160002727 | | 2017 | 24.614102704585 | | 2016 | 24.699181938804 | | 2015 | 24.780534116585 | | 2014 | 24.8755143158 | | 2013 | 24.965479771014 | | 2012 | 25.055763258127 | | 2011 | 25.146622318205 | | 2010 | 25.237347619894 | | 2009 | 25.31576221235 | | 2008 | 25.394402447613 | | 2007 | 25.472541969302 | | 2006 | 25.550590027805 | | 2005 | 25.631996052889 | | 2004 | 25.713079182208 | | 2003 | 25.789011998352 | | 2002 | 25.874414968544 | | 2001 | 25.951990825633 | | 2000 | 26.030133180152 | | 1999 | 26.097476422938 | | 1998 | 26.168630195212 | | 1997 | 26.239783971651 | | 1996 | 26.31093774809 | | 1995 | 26.382091516199 | | 1994 | 26.453245284309 | | 1993 | 26.516753694525 | | 1992 | 26.587886961671 | | 1991 | 27.637463018421 | | 1990 | 27.713902174215 |
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