| Year | Value | | 2012 | 21.018969546389 | | 2011 | 14.424960211246 | | 2010 | 12.173205462851 | | 2009 | 21.692771519328 | | 2008 | 44.331038407115 | | 2007 | 45.926821851852 | | 2006 | 43.97458088004 | | 2005 | 61.236204579811 | | 2004 | 76.04923191547 | | 2003 | 70.844277417726 | | 2002 | 58.623028293546 | | 2001 | 67.003147968382 | | 2000 | 54.9949320314 | | 1999 | 91.216350037397 | | 1998 | 95.517802786709 | | 1997 | 91.879527452745 | | 1993 | 43.512974051896 | | 1991 | 66.101694915254 | | 1990 | 73.333333333333 | | 1989 | 75 | | 1988 | 70.37037037037 | | 1987 | 72 |
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