| Year | Value | | 2021 | 11.724374357216 | | 2020 | 11.604388069935 | | 2019 | 11.484401782653 | | 2018 | 11.364415495372 | | 2017 | 11.24442920809 | | 2016 | 11.124442920809 | | 2015 | 10.970174837161 | | 2014 | 10.754542338018 | | 2013 | 10.538909838876 | | 2012 | 10.323277339733 | | 2011 | 10.10764484059 | | 2010 | 9.8920123414467 | | 2009 | 9.6850074277225 | | 2008 | 9.4780025139984 | | 2007 | 9.2709976002742 | | 2006 | 9.0639926865501 | | 2005 | 8.856987772826 | | 2004 | 8.6499828591018 | | 2003 | 8.4429779453777 | | 2002 | 8.2359730316535 | | 2001 | 8.0289681179294 | | 2000 | 7.8219632042052 | | 1999 | 7.4957147754542 | | 1998 | 7.1694663467032 | | 1997 | 6.8432179179522 | | 1996 | 6.5169694892012 | | 1995 | 6.1907210604502 | | 1994 | 5.8644726316992 | | 1993 | 5.5382242029482 | | 1992 | 5.2119757741972 | | 1991 | 4.8857273454462 | | 1990 | 4.5594789166952 |
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