| Year | Value | | 2012 | 42.519754301018 | | 2011 | 42.480722450522 | | 2010 | 38.766000296344 | | 2009 | 42.929792150955 | | 2008 | 43.287705434098 | | 2007 | 45.782470495042 | | 2006 | 48.563910464593 | | 2005 | 52.420529722242 | | 2004 | 53.837558093129 | | 2003 | 55.021315572241 | | 2002 | 55.934434002407 | | 2001 | 56.467819973288 | | 2000 | 56.7212758295 | | 1999 | 55.638636380338 | | 1998 | 54.281744033833 | | 1997 | 56.93532780669 | | 1996 | 55.29651794003 | | 1995 | 57.518267866149 | | 1994 | 59.03451415852 | | 1993 | 59.309827456864 | | 1992 | 55.49913175444 | | 1991 | 60.672718808194 | | 1990 | 54.770380095602 |
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