| Year | Value | | 2014 | 49.778239238013 | | 2013 | 53.571207771676 | | 2012 | 53.965122561002 | | 2011 | 53.317548224959 | | 2010 | 57.465748951983 | | 2009 | 53.970949978324 | | 2008 | 49.477606395625 | | 2007 | 45.743235700968 | | 2006 | 47.74708684248 | | 2005 | 46.803953655332 | | 2004 | 40.488147619872 | | 2003 | 37.450553698051 | | 2002 | 36.273019810774 | | 2001 | 41.357152746479 | | 2000 | 44.866925794004 | | 1999 | 48.589631114096 | | 1998 | 55.246587879428 | | 1997 | 55.703693916566 | | 1996 | 53.286180122836 | | 1995 | 54.449244046555 | | 1994 | 50.441923149251 | | 1993 | 50.442899968866 | | 1992 | 47.190870662436 | | 1991 | 54.697023498984 | | 1990 | 56.57485477248 | | 1989 | 61.602157120647 | | 1988 | 62.482207111499 | | 1987 | 62.771153802703 | | 1986 | 61.549197597674 | | 1985 | 62.995480851616 | | 1984 | 62.910392713046 | | 1983 | 64.896201725856 | | 1982 | 63.795705652269 | | 1981 | 66.224861240465 | | 1980 | 66.983499525564 | | 1979 | 64.993612792233 | | 1978 | 64.823837015029 | | 1977 | 66.442709843212 | | 1976 | 66.322263582208 | | 1975 | 64.658803254277 | | 1974 | 65.001215394838 | | 1973 | 64.344259749309 | | 1972 | 64.030292764769 | | 1971 | 61.936084884521 |
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