| Year | Value | | 2022 | 6.1470758840572 | | 2021 | 7.0226081524624 | | 2020 | 7.0424008512994 | | 2019 | 6.674263316045 | | 2018 | 7.2518619700397 | | 2017 | 8.1194012443605 | | 2016 | 9.1034863830255 | | 2015 | 10.020228452825 | | 2014 | 10.818024192062 | | 2013 | 11.320560947318 | | 2012 | 10.867696101802 | | 2011 | 9.9040851186127 | | 2010 | 9.8535866532807 | | 2009 | 9.1749942654434 | | 2008 | 7.2489855366108 | | 2007 | 7.4956121081358 | | 2006 | 8.6756728330633 | | 2005 | 9.6255460835335 | | 2004 | 9.8815258170881 | | 2003 | 9.6440011766708 | | 2002 | 9.8552711823809 | | 2001 | 9.6392168788372 | | 2000 | 9.8435710006331 | | 1999 | 10.194005141103 | | 1998 | 10.491587346327 | | 1997 | 10.901030875632 | | 1996 | 11.112036786164 | | 1995 | 11.080304417385 | | 1994 | 11.520004110209 | | 1993 | 10.951073720576 | | 1992 | 9.2948639779287 | | 1991 | 8.5520907019868 |
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