| Year | Value | | 2014 | 27.208508216527 | | 2013 | 25.669858000735 | | 2012 | 30.296253346564 | | 2011 | 32.308937076381 | | 2010 | 40.406057875987 | | 2009 | 30.578826989134 | | 2008 | 37.331650331167 | | 2007 | 39.004471086397 | | 2006 | 39.557929148558 | | 2005 | 43.329316029278 | | 2004 | 44.243679144003 | | 2003 | 45.048562454272 | | 2002 | 43.403727677302 | | 2001 | 43.089992474794 | | 2000 | 42.870271896652 | | 1999 | 44.066912379595 | | 1998 | 45.041646132143 | | 1997 | 47.914563942248 | | 1996 | 50.886220357467 | | 1995 | 50.14524075821 | | 1994 | 47.265060834324 | | 1993 | 48.419888644476 | | 1992 | 49.125308956557 | | 1991 | 52.993439575085 | | 1990 | 46.118504105142 |
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