Year | Value | 2021 | 1.7 | 2020 | 2.2 | 2019 | 2.6 | 2018 | 3.2 | 2017 | 3.3 | 2016 | 3.4 | 2015 | 3.9 | 2014 | 3.1 | 2013 | 3.2 | 2012 | 3.1 | 2011 | 2.7 | 2010 | 2.7 | 2009 | 2.1 | 2008 | 1.8 | 2007 | 1.7 | 2006 | 1.6 | 2005 | 1.9 | 2004 | 1.7 | 2003 | 2.1 | 2002 | 2.7 | 2000 | 3.5 | 1998 | 4 | 1995 | 3.5 | 1993 | 4.2 | 1991 | 1.7 | 1989 | 0.7 | 1987 | 2.7 | 1986 | 2.5 | 1984 | 2 | 1983 | 1.7 | 1982 | 1.2 | 1981 | 1.9 | 1980 | 2.5 | 1979 | 3.5 | 1978 | 4.2 | 1977 | 4 |
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