Year | Value | 2019 | 25.417700256729 | 2018 | 26.527917800035 | 2017 | 23.204978973268 | 2016 | 19.111669910384 | 2015 | 19.241188374901 | 2014 | 24.216842566797 | 2013 | 27.121423944515 | 2012 | 27.946183791027 | 2011 | 29.149131377402 | 2010 | 30.257661832862 | 2009 | 27.383629188641 | 2008 | 38.002483535216 | 2007 | 34.797726226691 | 2006 | 34.938045923052 | 2005 | 33.463803742651 | 1990 | 26.341096118319 | 1989 | 21.890125918949 | 1980 | 26.030401577636 | 1979 | 27.082079016446 | 1978 | 25.253224281429 | 1977 | 28.648562246952 |
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