| Year | Value | | 2021 | 39.548295433641 | | 2020 | 39.533294345536 | | 2019 | 39.514367180653 | | 2018 | 39.499820130394 | | 2017 | 39.481040667708 | | 2016 | 39.479288502766 | | 2015 | 39.461983228874 | | 2014 | 39.441805997589 | | 2013 | 39.422576891189 | | 2012 | 39.403686410505 | | 2011 | 39.384238603136 | | 2010 | 39.364757643588 | | 2009 | 39.381799450837 | | 2008 | 39.39861230866 | | 2007 | 39.414781430871 | | 2006 | 39.431044320165 | | 2005 | 39.462179696507 | | 2004 | 39.48255762684 | | 2003 | 39.500504665086 | | 2002 | 39.524415658718 | | 2001 | 39.542334955234 | | 2000 | 39.559354751583 | | 1999 | 39.579416281839 | | 1998 | 39.624976547362 | | 1997 | 39.666757738783 | | 1996 | 39.706859008002 | | 1995 | 39.745986373184 | | 1994 | 39.78279386256 | | 1993 | 39.817965482145 | | 1992 | 39.854465436618 |
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