| Year | Value | | 2020 | 0.13415507790385 | | 2019 | 0.13647089007679 | | 2018 | 0.1259292969962 | | 2017 | 0.14419174040873 | | 2016 | 0.13343241925949 | | 2015 | 0.072343719479993 | | 2014 | 0.074298824397075 | | 2013 | 0.075968518645873 | | 2012 | 0.078265117731333 | | 2011 | 0.13157671346836 | | 2010 | 0.13611577393014 | | 2009 | 0.13369116564465 | | 2008 | 0.1274824552271 | | 2007 | 0.12598668572705 | | 2006 | 0.12487299375926 | | 2005 | 0.12415317190662 | | 2004 | 0.12381882004792 | | 2003 | 0.12797875717765 | | 2002 | 0.1283691200214 | | 2001 | 0.18325132836389 | | 2000 | 0.18476813488746 | | 1999 | 0.18834660154838 | | 1998 | 0.195865417683 | | 1997 | 0.20473129255911 | | 1996 | 0.18423973473462 | | 1995 | 0.1961700381241 | | 1994 | 0.21602692991708 | | 1992 | 0.23112556416306 | | 1991 | 0.23848078202618 |
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