| Year | Value | | 2021 | 68.57209664848 | | 2020 | 68.485113016368 | | 2019 | 68.398129384256 | | 2018 | 68.311145752143 | | 2017 | 68.224006235386 | | 2016 | 68.083956386293 | | 2015 | 67.996884735202 | | 2014 | 67.910062305296 | | 2013 | 67.823239875389 | | 2012 | 67.736417445483 | | 2011 | 67.649595015576 | | 2010 | 67.56277258567 | | 2009 | 67.475732087227 | | 2008 | 67.388691588785 | | 2007 | 67.301651090343 | | 2006 | 67.2146105919 | | 2005 | 67.127570093458 | | 2004 | 67.040529595016 | | 2003 | 66.953489096573 | | 2002 | 66.866448598131 | | 2001 | 66.779408099688 | | 2000 | 66.692367601246 | | 1999 | 66.604579439252 | | 1998 | 66.516791277259 | | 1997 | 66.429003115265 | | 1996 | 66.341214953271 | | 1995 | 66.253426791277 | | 1994 | 66.165638629284 | | 1993 | 66.07785046729 | | 1992 | 65.990062305296 | | 1991 | 65.902274143302 | | 1990 | 65.449570474069 |
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