Year | Value | 2023 | 12.9 | 2021 | 12.9 | 2019 | 12.1 | 2018 | 12.5 | 2017 | 14 | 2016 | 14.5 | 2015 | 15.4 | 2014 | 16.8 | 2013 | 18.2 | 2012 | 18.8 | 2011 | 18.3 | 2010 | 21.7 | 2009 | 23 | 2008 | 23.2 | 2007 | 30.5 | 2006 | 33.9 | 2005 | 34.5 | 2004 | 34.7 | 2003 | 35.8 | 2002 | 37.1 | 2001 | 40 | 2000 | 35 | 1999 | 36.5 | 1998 | 38.7 | 1997 | 39.1 | 1995 | 39.3 | 1991 | 48.1 | 1989 | 50.1 | 1979 | 39.7 |
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