| Year | Value | | 2022 | 31.17907803595 | | 2021 | 30.663831582456 | | 2020 | 32.026820440338 | | 2019 | 33.688652516722 | | 2018 | 31.467573593551 | | 2017 | 30.957286946685 | | 2016 | 30.39685134013 | | 2015 | 38.899500285451 | | 2014 | 37.306482326732 | | 2013 | 39.829264889573 | | 2012 | 40.901532409716 | | 2011 | 39.658848747555 | | 2010 | 40.770763735788 | | 2009 | 41.929296178507 | | 2008 | 39.189074454336 | | 2007 | 39.536145578239 | | 2006 | 36.876673778069 | | 2005 | 36.939354044861 | | 2004 | 38.222252040249 | | 2003 | 35.988828191321 | | 2002 | 33.322854431621 | | 2001 | 35.327561872135 | | 2000 | 33.455696297098 | | 1999 | 32.119216488403 | | 1998 | 31.890159425631 | | 1997 | 31.754763990728 | | 1996 | 31.454143591856 | | 1995 | 31.371953070878 | | 1994 | 31.266790811097 | | 1993 | 31.233747841661 | | 1992 | 31.261990511684 | | 1991 | 31.267019849324 |
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