| Year | Value | | 2020 | 0.4417711801995 | | 2019 | 0.42944514563133 | | 2018 | 0.43134716825015 | | 2017 | 0.4336518144534 | | 2016 | 0.44269682241797 | | 2015 | 0.45323239633175 | | 2014 | 0.46412725355233 | | 2013 | 0.48137650632811 | | 2012 | 0.51604185433501 | | 2011 | 0.51003649601325 | | 2010 | 0.53982811304575 | | 2009 | 0.556241927682 | | 2008 | 0.50113111556923 | | 2007 | 0.50749580824322 | | 2006 | 0.57794276642363 | | 2005 | 0.70424345300236 | | 2004 | 0.67564029029594 | | 2003 | 0.70642745646275 | | 2002 | 0.70511200506474 | | 2001 | 0.71607852366694 | | 2000 | 0.72005084067206 | | 1999 | 0.7455804521665 | | 1998 | 0.74785160757907 | | 1997 | 0.74937781016679 | | 1996 | 0.7641477372116 | | 1995 | 0.80974634330889 | | 1994 | 0.89346537847732 | | 1993 | 0.94182476985243 | | 1992 | 1.0110119560273 | | 1991 | 1.034938242897 |
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