| Year | Value | | 2020 | 0.38829634672473 | | 2019 | 0.37278418632913 | | 2018 | 0.37713169325147 | | 2017 | 0.33646905670732 | | 2016 | 0.34741649104137 | | 2015 | 0.35531160135414 | | 2014 | 0.37418342712713 | | 2013 | 0.35587708987841 | | 2012 | 0.29174915079151 | | 2011 | 0.36845902941427 | | 2010 | 0.38593977282612 | | 2009 | 0.36585687960353 | | 2008 | 0.2905562925167 | | 2007 | 0.29493232064357 | | 2006 | 0.49749422302946 | | 2005 | 0.27474015468656 | | 2004 | 0.27430184693917 | | 2003 | 0.28284427594531 | | 2002 | 0.31064773054747 | | 2001 | 0.35399932053265 | | 2000 | 0.38615317283348 | | 1999 | 0.42988524841757 | | 1998 | 1.1883897520947 | | 1997 | 1.24656448056 | | 1996 | 1.6253477989872 | | 1995 | 1.6489535665633 | | 1994 | 0.45412644721016 | | 1993 | 0.46086409683111 | | 1992 | 0.46663898356821 | | 1991 | 0.5041640801999 |
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