| Year | Value | | 2021 | 27.360322809507 | | 2020 | 27.803742461866 | | 2019 | 28.247162114225 | | 2018 | 28.690581766584 | | 2017 | 29.134001418943 | | 2016 | 29.577421071302 | | 2015 | 30.020840723661 | | 2014 | 30.46426037602 | | 2013 | 30.907680028379 | | 2012 | 31.351099680738 | | 2011 | 31.794519333097 | | 2010 | 32.237938985456 | | 2009 | 32.681358637815 | | 2008 | 33.124778290174 | | 2007 | 33.568197942533 | | 2006 | 34.011617594892 | | 2005 | 34.455037247251 | | 2004 | 34.89845689961 | | 2003 | 35.341876551969 | | 2002 | 35.785296204328 | | 2001 | 36.228715856687 | | 2000 | 36.672135509046 | | 1999 | 37.292923022348 | | 1998 | 37.913710535651 | | 1997 | 38.534498048954 | | 1996 | 39.155285562256 | | 1995 | 39.776073075559 | | 1994 | 40.396860588861 | | 1993 | 41.017648102164 | | 1992 | 41.638435615466 | | 1991 | 42.259223128769 | | 1990 | 42.880010642072 |
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