| Year | Value | | 2021 | 54.962678049949 | | 2020 | 59.26726541967 | | 2019 | 56.092043954609 | | 2018 | 57.036544132453 | | 2017 | 58.666865876484 | | 2016 | 62.035782468322 | | 2015 | 63.033481097671 | | 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 | 67.000990990087 | | 1998 | 68.474129503291 | | 1997 | 64.184996610606 | | 1996 | 64.977462200585 | | 1995 | 64.970066105683 | | 1994 | 64.340194144803 | | 1993 | 69.082355667398 | | 1992 | 72.945611433098 | | 1991 | 72.147688583438 | | 1990 | 55.071507478291 | | 1989 | 56.592693768067 | | 1988 | 54.488677796422 | | 1987 | 52.39266743037 | | 1986 | 52.306480812724 | | 1985 | 46.1027970196 | | 1984 | 48.174338995208 | | 1983 | 46.096037713431 | | 1982 | 45.30760376835 | | 1981 | 41.568608010096 | | 1980 | 39.580029302546 |
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