| Year | Value | | 2021 | 0.35072951739618 | | 2020 | 0.35072951739618 | | 2019 | 0.35072951739618 | | 2018 | 0.35072951739618 | | 2017 | 0.35072951739618 | | 2016 | 0.35072951739618 | | 2015 | 0.35072951739618 | | 2014 | 0.35072951739618 | | 2013 | 0.35072951739618 | | 2012 | 0.35072951739618 | | 2011 | 0.35072951739618 | | 2010 | 0.35072951739618 | | 2009 | 0.34287317620651 | | 2008 | 0.33501683501683 | | 2007 | 0.32716049382716 | | 2006 | 0.31930415263749 | | 2005 | 0.31144781144781 | | 2004 | 0.30359147025814 | | 2003 | 0.29573512906846 | | 2002 | 0.28787878787879 | | 2001 | 0.28002244668911 | | 2000 | 0.27216610549944 | | 1999 | 0.26430976430976 | | 1998 | 0.25645342312009 | | 1997 | 0.24859708193041 | | 1996 | 0.24074074074074 | | 1995 | 0.23288439955107 | | 1994 | 0.22502805836139 | | 1993 | 0.21717171717172 | | 1992 | 0.20931537598204 | | 1991 | 0.20145903479237 | | 1990 | 0.19360269360269 |
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