| Year | Value | | 2020 | 0.15273991100817 | | 2019 | 0.15582261663287 | | 2018 | 0.15675974258155 | | 2017 | 0.16515189845861 | | 2016 | 0.16698583380317 | | 2015 | 0.17199614505677 | | 2014 | 0.17742583210046 | | 2013 | 0.18318404399131 | | 2012 | 0.18927189380725 | | 2011 | 0.19566762881996 | | 2010 | 0.20234006282659 | | 2009 | 0.20926031130184 | | 2008 | 0.2204129657326 | | 2007 | 0.22790013540376 | | 2005 | 0.24358437508096 | | 2004 | 0.24012310768698 | | 2003 | 0.25500777419534 | | 2002 | 0.2632058028106 | | 2001 | 0.271815558043 | | 2000 | 0.37022531133026 | | 1999 | 0.38202278517934 | | 1998 | 0.39423236664329 | | 1997 | 0.40691852877107 | | 1996 | 0.42008953655722 | | 1995 | 0.43381735680412 | | 1994 | 0.3300014708637 | | 1993 | 0.3407874917359 | | 1992 | 0.35188658125765 | | 1991 | 0.36333173121341 |
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