Year | Value | 2019 | 2.617 | 2018 | 2.425 | 2017 | 2.261 | 2016 | 2.158 | 2015 | 2.147 | 2014 | 2.069 | 2013 | 2.341 | 2011 | 2.702 | 2010 | 2.319 | 2007 | 2.326 | 2006 | 2.492 | 2001 | 2.621 | 1997 | 2.1 | 1993 | 1.862 | 1991 | 1.326 | 1989 | 1.862 | 1983 | 1.255 | 1981 | 1.714 | 1979 | 1.693 | 1970 | 0.726 | 1965 | 0.938 | 1960 | 0.778 |
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