| Year | Value | | 2020 | 0.42067814696563 | | 2019 | 0.41409969864344 | | 2018 | 0.41288231046938 | | 2017 | 0.41078044907797 | | 2016 | 0.41108884029221 | | 2015 | 0.41560568645155 | | 2014 | 0.42064713240422 | | 2013 | 0.43008090306235 | | 2012 | 0.44548109425544 | | 2011 | 0.46969480022694 | | 2010 | 0.59944931189017 | | 2009 | 0.59903098314547 | | 2008 | 0.58209592225107 | | 2007 | 0.58287801562333 | | 2006 | 0.59002546127759 | | 2005 | 0.69107664139371 | | 2004 | 0.70929379163636 | | 2003 | 0.70706217678622 | | 2002 | 0.73895369698659 | | 2001 | 0.77043761905997 | | 2000 | 0.55461070505018 | | 1999 | 0.82697290814267 | | 1998 | 0.83756304765259 | | 1997 | 0.87320842587011 | | 1996 | 0.96856864672826 | | 1995 | 0.9243133719124 | | 1994 | 0.91337871984522 | | 1993 | 1.0055186298348 | | 1992 | 1.1159910329868 | | 1991 | 1.1481235666356 |
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