| Year | Value | | 2014 | 22.730089233038 | | 2013 | 28.459619795711 | | 2012 | 32.446098736585 | | 2011 | 35.372746570174 | | 2010 | 32.56202009249 | | 2009 | 28.854920088074 | | 2008 | 28.99464869636 | | 2007 | 30.600710471135 | | 2006 | 26.310701135556 | | 2005 | 27.692547009639 | | 2004 | 25.404655035247 | | 2003 | 20.815961049409 | | 2002 | 24.872425387149 | | 2001 | 26.311782075109 | | 2000 | 29.226363998224 | | 1999 | 21.111303904365 | | 1998 | 23.072714899198 | | 1997 | 20.357282167402 | | 1996 | 36.437848950741 | | 1995 | 45.330641124142 | | 1994 | 47.170714575398 | | 1993 | 15.60340173551 | | 1992 | 18.126435611228 | | 1991 | 31.573246451425 | | 1990 | 34.38924098794 |
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