| Year | Value | | 2020 | 0.55933691563617 | | 2019 | 0.29028499074544 | | 2018 | 0.29633860947764 | | 2017 | 0.25935366185758 | | 2016 | 0.26254310758707 | | 2015 | 0.23829115680403 | | 2014 | 0.2143885142441 | | 2013 | 0.18888918591802 | | 2012 | 0.12795959888931 | | 2011 | 0.20414764159067 | | 2010 | 0.21023172727252 | | 2009 | 0.21643016698077 | | 2008 | 0.22022943135109 | | 2007 | 0.22710665553087 | | 2006 | 0.23438351471362 | | 2005 | 0.241968705784 | | 2004 | 0.22892091053084 | | 2003 | 0.26228876617215 | | 2002 | 0.33775030741944 | | 2001 | 0.34913081357356 | | 2000 | 0.36070130775581 | | 1999 | 0.37213911931319 | | 1998 | 0.38218459743096 | | 1997 | 0.3925963837079 | | 1996 | 0.40325212224694 | | 1995 | 0.41234887210376 | | 1994 | 0.33253100990222 | | 1993 | 0.3394887356223 | | 1992 | 0.34616659440439 | | 1991 | 0.38186740799859 |
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