Year | Value | 2021 | 14.963848819492 | 2020 | 14.1842862707 | 2019 | 14.560555204924 | 2018 | 14.38335467718 | 2017 | 15.586663859467 | 2016 | 17.112125197642 | 2015 | 18.918308998916 | 2014 | 17.939831634066 | 2013 | 17.761460563275 | 2012 | 17.157213939798 | 2011 | 17.216303110013 | 2010 | 16.242680715695 | 2009 | 15.272830152286 | 2008 | 16.785344992707 | 2007 | 17.539525726519 | 2006 | 17.947057234366 | 2005 | 17.468056929136 | 2004 | 17.421266157802 | 2003 | 17.774763752777 | 2002 | 16.489100061404 | 2001 | 16.633416076476 | 2000 | 17.962709479419 | 1999 | 17.056618970221 | 1998 | 17.736038716267 | 1997 | 17.036011623484 | 1996 | 16.107730270379 | 1995 | 17.402044516858 | 1994 | 17.787142835645 | 1993 | 19.66235438565 | 1992 | 22.412923770981 | 1991 | 22.52189300785 | 1990 | 23.056300268096 | 1989 | 5.1175 | 1988 | 4.5262543757293 | 1987 | 4.4633771151343 | 1986 | 4.4645838301932 | 1985 | 4.2018348623853 | 1984 | 4.0521994853572 | 1983 | 4.0249772342917 | 1982 | 4.0747869122904 | 1981 | 4.3883277216611 |
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