| Year | Value | | 2020 | 5.3876299615515 | | 2019 | 5.4730962729842 | | 2018 | 5.6319163213154 | | 2017 | 5.4655605652716 | | 2016 | 7.1674813121036 | | 2015 | 6.4459031929869 | | 2014 | 6.1675217644257 | | 2013 | 3.5599159859827 | | 2012 | 3.1836926255663 | | 2011 | 2.83822424746 | | 2010 | 6.647499435045 | | 2009 | 6.7739050352302 | | 2008 | 6.729230046868 | | 2007 | 6.9113526809844 | | 2006 | 7.2448502845365 | | 2005 | 7.8313356211124 | | 2004 | 7.9503530148313 | | 2003 | 8.3265278106029 | | 2002 | 8.4473862362601 | | 2001 | 8.6198305128337 | | 2000 | 8.6748812564365 | | 1999 | 9.0698834519976 | | 1998 | 9.5942291160196 | | 1997 | 9.9763132487771 | | 1996 | 12.828083074569 | | 1995 | 13.408542377812 | | 1994 | 8.2535277383013 | | 1993 | 10.757788652168 | | 1992 | 11.185170218826 | | 1991 | 11.531645605397 |
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