| Year | Value | | 2020 | 0.7488512209518 | | 2019 | 0.70555801847568 | | 2018 | 0.71806847557561 | | 2017 | 0.69712404150577 | | 2016 | 0.70878084050448 | | 2015 | 0.71890222378877 | | 2014 | 0.73221692752041 | | 2013 | 0.72410539953486 | | 2012 | 0.73412214937318 | | 2011 | 0.75143977685394 | | 2010 | 0.74813740545679 | | 2009 | 0.74550955825946 | | 2008 | 0.76754951396976 | | 2007 | 0.77751783352 | | 2006 | 0.82196221108314 | | 2005 | 0.74283069865192 | | 2004 | 0.78009897786822 | | 2003 | 0.78523284486687 | | 2002 | 0.79902701013956 | | 2001 | 0.82650057459101 | | 2000 | 0.8484227585246 | | 1999 | 0.87594744506935 | | 1998 | 0.93435876015185 | | 1997 | 0.95995910900442 | | 1996 | 0.96921724172821 | | 1995 | 0.96534938931864 | | 1994 | 0.43071918317017 | | 1993 | 0.4419351684094 | | 1992 | 0.45345419807743 | | 1991 | 0.46368829458196 |
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