| Year | Value | | 2020 | 0.40707711709614 | | 2019 | 0.38862268235148 | | 2018 | 0.40654719870686 | | 2017 | 0.42822462779786 | | 2016 | 0.42678354148467 | | 2015 | 0.41173235548299 | | 2014 | 0.4091852912084 | | 2013 | 0.4193132248396 | | 2012 | 0.42207431436612 | | 2011 | 0.45597471108419 | | 2010 | 0.47556978598389 | | 2009 | 0.47466591753406 | | 2008 | 0.49073998191132 | | 2007 | 0.49692601566708 | | 2006 | 0.51450439335302 | | 2003 | 0.94932237926993 | | 2002 | 1.4910405160036 | | 2001 | 1.2850280153711 | | 2000 | 0.95100942857919 | | 1999 | 0.96601569336404 | | 1998 | 0.9957126166487 | | 1997 | 1.0544435208554 | | 1996 | 1.1883166467758 | | 1995 | 1.1821193502722 | | 1994 | 0.61273289594417 | | 1993 | 0.63718669331169 | | 1992 | 0.6670808126712 | | 1991 | 0.67679604751108 |
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