| Year | Value | | 2021 | 11.468518282587 | | 2020 | 10.865896382049 | | 2019 | 10.594397514508 | | 2018 | 9.9923900838434 | | 2017 | 10.939623860491 | | 2016 | 12.097283641196 | | 2015 | 12.336506941829 | | 2014 | 12.610966606719 | | 2013 | 12.452902755808 | | 2012 | 12.952841512741 | | 2011 | 12.663627701231 | | 2010 | 12.853042690326 | | 2009 | 12.383041559416 | | 2008 | 13.317846357403 | | 2007 | 12.4482684483 | | 2006 | 12.878886695432 | | 2005 | 13.103175645985 | | 2004 | 13.100779899439 | | 2003 | 12.518779700295 | | 2002 | 9.8189583466632 | | 2001 | 9.3248987939006 | | 2000 | 9.622603501889 | | 1999 | 9.0761243355918 | | 1998 | 9.0305261863884 | | 1997 | 8.6900863555499 | | 1996 | 8.1717877749291 | | 1995 | 8.0543576517231 | | 1994 | 8.126437228092 | | 1993 | 8.0151380055567 | | 1992 | 5.5479221344114 | | 1991 | 5.0082365474401 | | 1990 | 4.838513146697 |
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