| Year | Value | | 2018 | 46.522498664923 | | 2017 | 47.583609380382 | | 2016 | 47.633755591125 | | 2015 | 49.964718385147 | | 2014 | 49.900924873031 | | 2013 | 50.311827361088 | | 2012 | 50.678030551448 | | 2011 | 51.556553659921 | | 2010 | 51.591910300254 | | 2009 | 55.256446112231 | | 2008 | 57.292214280579 | | 2007 | 57.497536388895 | | 2006 | 59.666730275801 | | 2005 | 62.226526100688 | | 2004 | 62.592976742406 | | 2003 | 62.190053896046 | | 2002 | 62.552771294557 | | 2001 | 59.017909796885 | | 2000 | 55.004246496455 | | 1999 | 51.352951438415 | | 1998 | 50.319218173514 | | 1997 | 50.365436127615 | | 1996 | 45.723307702808 | | 1995 | 47.49164130283 | | 1994 | 49.594282704727 | | 1993 | 51.759808288675 | | 1992 | 49.680901359464 | | 1991 | 50.010080358357 | | 1990 | 50.783253794831 |
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