Year | Value | 2020 | 14.765397230424 | 2015 | 17.344472061159 | 2014 | 16.542638243449 | 2013 | 15.063241908815 | 2012 | 14.747472315507 | 2011 | 14.787978788626 | 2010 | 14.425098400861 | 2009 | 14.161970190711 | 2008 | 16.130515984298 | 2007 | 16.385000548022 | 2006 | 15.238356084697 | 2005 | 14.534953963975 | 2004 | 14.495859325418 | 2003 | 13.746465776675 | 1981 | 8.6438943269716 | 1980 | 8.8139086111851 | 1979 | 8.1370500972688 | 1978 | 7.9005771146285 | 1977 | 13.093741033056 | 1976 | 11.661721500806 | 1975 | 11.085409252669 | 1974 | 11.121314644756 | 1973 | 10.827397853556 | 1972 | 10.672478871263 |
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