Year | Value | 2019 | 2.57 | 2018 | 2.62 | 2017 | 2.73 | 2016 | 2.74 | 2015 | 2.72 | 2014 | 2.76 | 2013 | 2.78 | 2012 | 2.83 | 2011 | 2.82 | 2010 | 2.75 | 2009 | 2.41 | 2002 | 6.2 | 1998 | 6.1999998093 | 1997 | 6.0999999046 | 1996 | 6.0999999046 | 1995 | 6.1999998093 | 1994 | 6.6999998093 | 1993 | 6.5 | 1992 | 7.0999999046 | 1991 | 7.4000000954 | 1990 | 8.5 | 1985 | 9.5 | 1980 | 10.199999809265 | 1970 | 10.800000190735 | 1960 | 11.699999809265 |
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