Year | Value | 2019 | 25.283297196794 | 2018 | 26.3540074843 | 2017 | 23.066164645939 | 2016 | 18.995469486548 | 2015 | 19.121683051926 | 2014 | 23.97218298728 | 2013 | 26.82034876922 | 2012 | 27.626133982405 | 2011 | 28.696957376414 | 2010 | 29.915030537592 | 2009 | 27.090623547788 | 2008 | 37.832809435555 | 2007 | 34.519042404726 | 2006 | 34.425526050188 | 2005 | 32.940432940004 | 1990 | 26.341096118319 | 1989 | 21.890125918949 | 1980 | 26.030401577636 | 1979 | 27.082079016446 | 1978 | 25.253224281429 | 1977 | 28.648562246952 |
|