| Year | Value | | 2021 | 27.579034941764 | | 2020 | 27.995008319468 | | 2019 | 28.057404326123 | | 2018 | 28.036605657238 | | 2017 | 27.932612312812 | | 2016 | 28.015806988353 | | 2015 | 28.077035065097 | | 2014 | 28.269550748752 | | 2013 | 28.314756280153 | | 2012 | 28.953169189819 | | 2011 | 28.930294460156 | | 2010 | 28.945124867439 | | 2009 | 28.737783322936 | | 2008 | 28.731808731809 | | 2007 | 28.627858627859 | | 2006 | 28.648648648649 | | 2005 | 28.918918918919 | | 2004 | 28.960498960499 | | 2003 | 29.370193307005 | | 2002 | 29.313929313929 | | 2001 | 29.97920997921 | | 2000 | 31.767151767152 | | 1999 | 31.995841995842 | | 1998 | 32.162162162162 | | 1997 | 32.224532224532 | | 1996 | 32.286902286902 | | 1995 | 32.370062370062 | | 1994 | 32.453222453223 | | 1993 | 32.474012474012 |
|