| Year | Value | | 2020 | 0.33194326754079 | | 2019 | 0.32696130505433 | | 2018 | 0.34716921200269 | | 2017 | 0.34610087829654 | | 2016 | 0.34528072458043 | | 2015 | 0.36415589846275 | | 2014 | 0.3836872439003 | | 2013 | 0.38418956110623 | | 2012 | 0.38424110924454 | | 2011 | 0.37837738108582 | | 2010 | 0.38046238108639 | | 2009 | 0.37970649276042 | | 2008 | 0.37159723038602 | | 2007 | 0.37175673161594 | | 2006 | 0.46558961053613 | | 2005 | 0.4880605113721 | | 2004 | 0.4926198482136 | | 2003 | 0.49650917901286 | | 2002 | 0.50430197339984 | | 2001 | 0.51531084411674 | | 2000 | 0.53415743123609 | | 1999 | 0.52881724659871 | | 1998 | 0.53589422688094 | | 1997 | 0.51836173846007 | | 1996 | 0.59832990308461 | | 1995 | 0.60634088601182 | | 1994 | 0.43611084870865 | | 1993 | 0.45682732278488 | | 1992 | 0.48212780380833 | | 1991 | 0.49440638809639 |
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