| Year | Value | | 2021 | 54.962678049949 | | 2020 | 59.26726541967 | | 2019 | 56.092043954609 | | 2018 | 57.036544132453 | | 2017 | 58.583955484048 | | 2016 | 62.064956870057 | | 2015 | 63.186164672669 | | 2014 | 56.621750580303 | | 2013 | 56.322681784151 | | 2012 | 53.447318483204 | | 2011 | 52.915064695009 | | 2010 | 54.111265914302 | | 2009 | 54.88784048734 | | 2008 | 45.779586854654 | | 2007 | 43.712854079565 | | 2006 | 47.438482621637 | | 2005 | 53.790154957164 | | 2004 | 63.007082674347 | | 2003 | 60.229627797403 | | 2002 | 62.7687709999 | | 2001 | 64.095346735604 | | 2000 | 60.872742212375 | | 1999 | 76.18397574549 | | 1998 | 77.859016816481 | | 1997 | 72.98202685117 | | 1996 | 73.883104819906 | | 1995 | 73.874696456975 | | 1994 | 73.158494642281 | | 1993 | 78.550606045108 | | 1992 | 82.943349753695 | | 1991 | 82.036066140462 | | 1990 | 62.619466800805 | | 1989 | 64.34914297515 | | 1988 | 61.956755980174 | | 1987 | 59.573471818525 | | 1986 | 59.475472684499 | | 1985 | 52.421527929503 | | 1984 | 54.776990125979 | | 1983 | 52.413842210196 | | 1982 | 51.517347534287 | | 1981 | 47.265894623821 | | 1980 | 45.00476642777 |
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