| Year | Value | | 2020 | 0.42974709383528 | | 2019 | 0.41600279553879 | | 2018 | 0.52418227564999 | | 2017 | 0.41680039012517 | | 2016 | 0.50876992152224 | | 2015 | 0.51780829011073 | | 2014 | 0.52757688333956 | | 2013 | 0.53802732282088 | | 2012 | 0.54891018457105 | | 2011 | 0.56033657550302 | | 2010 | 0.5724344204817 | | 2009 | 0.58514036054399 | | 2008 | 0.49972515116686 | | 2007 | 0.51272848463096 | | 2005 | 0.54120754226831 | | 2004 | 0.55674017492776 | | 2003 | 0.74522482859829 | | 2002 | 0.76806276845271 | | 2001 | 0.79233990162795 | | 2000 | 0.75523472065756 | | 1999 | 0.78001092015288 | | 1998 | 0.7721074505012 | | 1997 | 0.7979572294925 | | 1996 | 0.8248990395306 | | 1995 | 0.85250859921718 | | 1994 | 0.76561471205231 | | 1993 | 0.78995805322737 | | 1992 | 0.81341152929502 | | 1991 | 0.83429973052119 |
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