Year | Value | 2018 | 2.2845698600506 | 2017 | 2.2679697761175 | 2016 | 2.4429607529472 | 2015 | 2.3611556974687 | 2014 | 2.2855076468007 | 2013 | 2.1768497950206 | 2012 | 2.1568863681392 | 2011 | 1.9820999467603 | 2010 | 2.3050493366478 | 2009 | 2.2652086699327 | 2008 | 2.1563729272725 | 2007 | 2.3047573367641 | 2006 | 1.9383645843636 | 2005 | 1.7809608523404 | 2004 | 2.0143798397052 | 2003 | 2.1286411288416 | 1994 | 2.6493553048719 | 1993 | 2.2586946912119 | 1992 | 3.3745883545037 | 1991 | 5.5953172461444 | 1990 | 7.9108568704564 | 1989 | 7.2865126543979 | 1988 | 7.1016104156953 | 1987 | 3.9537677871568 |
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